Cognitive remediation therapy (CRT), also referred to as cognitive rehabilitation or cognitive enhancement,^[1] has been defined by the Cognitive Remediation Experts Workshop as a ″behavioral-training based intervention that aims to improve cognitive processes (attention, memory, executive function, social cognition, or metacognition) with the goal of durability and generalization″.^[2] CRT also aims to affect the domains of working memory, cognitive flexibility, and problem solving, ultimately intending to improve functioning in everyday life. Cognitive remediation is used to treat the deficits in neurocognitive abilities that may have resulted from a range of neurological and psychiatric disorders or from other brain injuries. CRT aims to take advantage of the brain’s plasticity, or its ability to change, in order to improve deficits in abilities.^[2][3]

The theory of applying methods to improve cognitive deficits has been discussed as early as 1896.^[4] However, the earliest documented examples of CRT date back to World War I, during which time soldiers returning from war evidenced brain injuries necessitating assessment and rehabilitation.^[5][6] Clinics treating these soldiers developed internationally in Germany, Great Britain, and Russia,^[5][6] with the famed Soviet neuropsychologist Alexander Luria providing much information about injury-related brain dysfunction.^[7] In particular, Luria assessed the current functioning of soldiers on a neurosurgical unit, investigated medications that could improve memory skills, and identified the functions of various brain regions.^[5]

Within the United States, the rehabilitation field was developing with psychologists such as Shepherd Franz commenting on related “reeducation” techniques.^[5][6] Others, such as Kurt Goldstein continued studying soldiers who had sustained brain injuries, noting their restrictions and suggesting psychotherapy treatments as remedies.^[7] Later advances in neurocognition and cognitive psychology in the 1960s led to the modern remediation methods used today,^[5] with the burgeoning field of neuropsychology and its testing tools aiding in the assessment of cognitive deficits needing intervention.^[7] For example, the earliest known study on CRT in psychotic patients dates back to 1973.^[8] The additional advances in modern technology throughout the 1980s and 1990s, in particular, the development of computers and video gaming systems (e.g., Atari) allowed for the introduction of educational and rehabilitation software that could be used with individuals who had experienced traumatic brain injuries.^[9] Although current CRT iterations were developed in the early 1990s, the accepted, formalized definition above was not ratified until 2010 by the Cognitive Remediation Experts Workshop.^[2]

One CRT technique is to teach individuals "errorless learning," or learning to complete tasks in structured situations that minimize the number of errors that can be made.^[2] This can be accomplished by initially presenting a task very slowly and then increasing the speed, or by breaking down a task into smaller, simpler steps.^[2] Other technique are "self-monitoring," for which the individual is taught to develop routines for remembering instructions and completing the task, and "scaffolding," where assistance is provided based on the person’s level of competency and is altered as the skill grows.^[2] CRT can focus on extended practice on a single task, or can involve multiple tasks and strategies intended to improve functioning on a particular skill.^[2] Cognitive training is provided either though computer-based tasks or pencil-and-paper activities, during which either an examiner or a computer-based program will provide feedback and alter task difficulty.^[10]

In order to determine which tasks should be used to address deficits in certain cognitive abilities, researchers rely on several assumptions of CRT, which one group deemed the "higher-order assumption," the "central-deficit assumption," and the "task-purity assumption".^[11] The higher-order assumption refers to the idea that certain functions are targeted for treatment because they are thought to influence several downstream cognitive processes; therefore, improvement in this function would lead to improvement in many others.^[11] The central-deficit assumption states that the deficit targeted by CRT must be one that is centrally related to the disorder in question.^[11] Lastly, that the training exercise is known to target the impaired ability.^[11] Although these assumptions are often employed by researchers, the research highlights some theoretical weakness regarding the validity of them.^[11]

CRT aims to improve cognition to a noticeable, long lasting extent in one of three main ways: helping to regain lost skills, aiding in the acquiring of new skills, or improving global functioning.^[2][12] It does so by affecting and altering existing neural pathways in the brain.^[12] In a typical brain, regions communicate with one another through connections established by neural synapses.^[13] These highly organized connections^[14] become damaged or atypical due to various psychiatric/neurological disorders,^[15][16] and can cause observable cognitive deficits associated with those disorders. However, due to the brain’s plasticity, or the ability of experience to modify brain structures and corresponding function, neural circuitry can be altered in many ways to restore such deficits.^[16][17][18] By providing an enriched environment, CRT has been shown to facilitate such neural plasticity and promote recovery.^[12][19]

For example, a recent review of the neural substrates altered by CRT in schizophrenia (SZ) patients showed significant post-CRT increases in activation within frontal brain regions such as the prefrontal cortex, as well as in changes in limbic, parietal, temporal, and parahippocampal areas using functional magnetic resonance imaging (fMRI) techniques.^[10] Other studies on SZ patients revealed increased activation in regions associated with working memory following CRT as compared to both SZ patients receiving control therapy and healthy controls.^[20] These network activation patterns appear not just to improve, but to normalize toward the patterns observed in healthy controls.^[21] Similarly, among patients with mood disorders, increased activation in lateral and medial prefrontal, lateral parietal, hippocampal, and superior temporal regions was observed on a memory task following CRT.^[22]

Structural MRI techniques have revealed changes in gray matter volume in medial temporal areas of SZ patients (e.g., amygdala, hippocampus, anterior cingulate cortex) following CRT, namely that CRT appears to have neuroprotective effects of reducing gray matter loss in those regions or even facilitating localized increases in gray matter volume.^[10] Changes to white matter organization have also been reported via diffusion tensor imaging techniques,^[10] including increased white matter integrity within the corpus callosum.^[21]

These neural changes are then measured by comparing pre-CRT performance on standardized neuropsychological tests to performance on these tests following CRT, with the goal to find improvements in the areas examined.^[2][12] Indeed, observed neural changes often correlate with such enhancements in neurocognitive performance.^[10]

Overall, CRT has been reported to have small to moderate effects on global cognition, social cognition, verbal working memory, and daily functioning that at times appear relatively long-lasting.^[10] However, some differences within individual psychiatric conditions exist.

The largest CRT literature on severe mental illness exists among the schizophrenia (SZ) cohort^[23] in part due to the inability of other existing treatments to address the persistent declines in cognition often observed in psychosis-spectrum disorders.^[24] Computerized CRT has been shown to increase attention, processing speed, verbal memory and working memory with small effect sizes, with the largest (medium) effect size observed in the improvement in social cognition; results were independent of whether or not these domains were specifically targeted by CRT tasks.^[25] Treatment duration, remediation approach, and training delivery method (e.g., computerized or not) were reported not have an effect on cognitive changes, but functioning outcome appears most affected by the increased clinical stability of patients and the conjunction of CRT with other treatment options.^[26] Post-CRT increases in cognitive flexibility and working memory have also been observed among comorbid populations, such as individuals with both SZ and social behavior problems, with improvements in the working memory predicting increase social functioning.^[27] Extended studies with a 2-year training period have continued to show improved neurocognition, processing speed, social cognition, social adjustment and cognitive style.^[1]

Cognitive improvements in working memory, reasoning, problem-solving and processing speed have also led to increased self-esteem and better quality of life as endorsed by patients.^[28] CRT has also improved patients’ level of insight into their symptoms and treatment by targeting episodic autobiographical memory and metacognition.^[29] These cognitive improvements resulting from CRT appear to persist, particularly in the memory domain, as they are apparent at a 6-month follow-up evaluation; some aspects of social functioning remain improved at follow-up as well while immediate post-CRT increases in self-esteem did not.^[30]

The timing of CRT was also considered within a SZ cohort; the effects of 12 weeks of CRT were compared between early-course patients (e.g., within five years of their initial psychotic episode) and chronic patients (more than 15 years of illness).^[31] While both groups improved cognitively, the early-course cohort demonstrated greater gains in processing speed and executive functioning, as well as better post-treatment adaptive function and real-world work skills.^[31] The authors concluded that CRT is most effective on its own in SZ when it is delivered early in the intervention phase.^[31] Relatedly, the effects of CRT appear limited in older individuals diagnosed with SZ as compared to younger ones, regardless of initial intelligence.^[32] However, other work has showed significant improvements in memory, executive function, and social functioning among chronic patients below the age of 55 years that persisted at 6-month follow-up evaluations, suggesting that CRT is still feasible in this group.^[33]

The benefits of CRT have also been demonstrated in disorders related to SZ, such as schizoaffective disorder.^[34] Other variants of SZ have equally benefitted from CRT, which has also been implemented in early-onset schizophrenia (EOS) patients who develop overt psychotic symptoms prior to the age of 18.^[35][36][37] In a group of 21 adolescents who received three months of CRT, individuals showed improvements in cognitive flexibility that led to decreased symptomatology and better social functioning as compared to a group receiving standard care.^[35] When combined with treatment-as-usual, a randomized controlled trial of 50 EOS individuals receiving CRT led to increased verbal memory ability and executive functions, improved daily living and adaptive functioning, and decreased family burden that were not observed among non-CRT treatment-as-usual controls.^[36] While the cognitive gains were maintained after three months, however, the functional changes were not.^[36] Gains in visuospatial abilities from CRT have also been reported in among EOS individuals and those identified as being putatively at clinical-high risk (CHR) for psychosis, above and beyond those associated with a computer games control group.^[37] Other preliminary work with CHR individuals, who also evidence cognitive deficits, have shown trends towards improved working memory and social functioning after CRT, though the authors caution about their likely underpowered study.^[38]

CRT among individuals with SZ also appears to have positive societal outcomes; cognitive improvements have been associated with reduced depressive symptoms, which subsequently predicts a reduction in health care costs, day care costs, and special accommodations costs (e.g., costs associated with residential care or psychiatric rehabilitation wards).^[39]

There is a large body of research addressing CRT as a treatment for the cognitive deficits associated with anorexia nervosa (AN), an eating disorder, such as cognitive inflexibility (e.g., the ability to switch between strategies and multitask), and extreme detail-oriented thinking that leads to restrictive eating.^[40][41][42] CRT for AN, the creation of which has been credited to Tchanturia and Davies,^[40] has been described as broadly targeting cognitive style (thought process) rather than focusing on the more specific symptoms of emotions, weight, or eating (thought content).^[41][43] CRT for AN has also been reported to have low drop-out rates, suggesting that this is a promising treatment approach among a cohort that usually has difficulty engaging in therapy.^[41][44] Participants across studies express direct interest in the treatment and have endorsed positive change in their lives following CRT.^[42][45] Successful implementation of CRT has occurred across the world, including in England,^[42][46][47] France,^[48] Norway,^[49][50] Italy,^[51] Germany,^[52] and the United States.^[53]

In particular, CRT for AN adults has improved cognition on a range of neuropsychological tasks, particularly those assessing for set-shifting flexibility.^[51] Significant increases in weight, body mass index scores, global functioning, and eating disorder symptoms like impulse control have also been reported, though perfectionism and depressive symptoms appear unaffected.^[51] AN-specific CRT appears more advantageous for this group as compared to nonspecific neurocognitive training, as a randomized controlled trial (RCT) contrasting the two reported significantly greater improvements in cognitive set-shifting among women who received the CRT versus the nonspecific treatment.^[52] An RCT comparing outpatient CRT with cognitive behavioral therapy (CBT) also showed greater cognitive improvement and fewer drop outs in the CRT group.^[53]

CRT has been effective for AN across different ages, helping not only adults but adolescents as well.^{[44][46][49][50]} For example, CRT appears to lead to significant weight gain, decreased depressive symptoms, and improved visuospatial memory, verbal abilities, and perceptual abilities.^[49] CRT has also shown to decrease self-reported and parent-reported executive dysfunction^[50] and increase self-reported cognitive flexibility and treatment engagement, particularly when patients believe it is important to change.^[46] This treatment appears effective for both inpatient and outpatient adolescents, and can accommodate individual tailoring of the intervention based on cognitive styles, age, and developmental status to reduce boredom and other negative associations.^[44]

CRT has also demonstrated preliminary efficacy in treating AN symptoms when presented in a group format,^[45][54] though more recent work has suggested an individual format is preferred.^[44] For example, an inpatient unit cohort of adolescents ages 13 to 19 received 10 sessions of group CRT targeting several cognitive domains such as attention and planning; after each training session, the group discussed the pros and cons of different thinking styles.^[45] Post-treatment changes were observed in cognitive flexibility and task performance.^[45] Other work has demonstrated comparable changes in self-reported flexibility following group CRT, as well as increased self-reported motivation and confidence to change.^[54] Additionally, early work on CRT implemented with families of a young person with AN revealed post-CRT improvements in communication and cooperation among family members, increased patient engagement in the treatment process, increased family knowledge of AN-related cognitive deficits, and decreased symptomatology of patients.^[43]

Mood disorders such as Major Depressive Disorder(MDD) have been associated with cognitive impairment in a wide range of executive function and neuropsychological tasks such as those assessing attention, memory, working memory, and psychomotor skills.^[55] Similar deficits in processing speed, attention, memory, and executive functioning have been reported in bipolar disorder as well.^[56] There is some effect of diagnostic variability, with greater cognitive deficits accompanying bipolar disorder(BP) than unipolar depression (MDD), and mood disorders with psychotic features showing the greatest impairments.^[55] Some of the cognitive dysfunction appears to persist even after clinical symptoms have remitted,^[55] necessitating the use of tools such as CRT to combat these effects.

A recent review of CRT for mood disorders revealed improvements in depressive symptoms and psychosocial functioning, as well as increased occupational functioning that correlated with better executive functioning, following remediation in individuals with BP.^[56] However, people with more severe cognitive functioning prior to treatment appeared to benefit less from CRT, suggesting that CRT may need to be more individualized for those with greater impairments.^[56] Given the paucity of current research addressing the benefits of CRT for BP, replication of such findings among independent samples is recommended.^[56]

Much more work has been done reviewing the effects of CRT on individuals with depression though with inconsistent findings reported; increases in executive functioning and decreases in depressive symptoms and rumination among adults with MDD have been suggested after remediation intervention.^[56] Among a relatively small group of 12 patients with recurrent MDD who received computerized CRT (versus healthy controls and a non-CRT treatment MDD group), improvements were observed across many tasks including those assessing executive function, psychomotor speed, attention, and verbal learning and memory; no changes in depressive symptoms were reported.^[57] CRT has been additionally shown as beneficial for verbal memory, attention, and processing speed in a group of 33 adults with treatment-resistant MDD for whom other treatment methods were not successful at fully alleviating symptoms.^[58] However, no improvements in executive functioning or changes in everyday functioning and behavior were found, suggesting that skills training or other remediation might be necessary for those effects.^[58] Given these inconsistencies in the literature, a recent review by Porter et al. (2013) suggested that sample sizes have been too small to be conclusive in their findings, but that additional research using more well-defined criteria is warranted to continue to assess the impact of CRT on mood disorders.^[59]

Interestingly, CRT has also been suggested as a potentially effective and beneficial tool for remedying the side effects of a more aggressive form of MDD treatment, electroconvulsive therapy (ECT).^[60] ECT can cause treatment-induced memory deficits in some individuals which has negative effects on their reported quality of life.^[60] Pilot data suggested that a modified version of CRT, Memory Training for ECT, was easy to implement in the ECT treatment community and was well-received by patients.^[60]

The negative effects of substance use on cognition and brain development have been well documented especially in the domains of memory and attention,^{[61][62][63][64][65][66]} with particular detrimental effects observed in adolescents.^[67][68] CRT has recently been employed as a potential mechanism to address these issues, and has been shown to be beneficial for individuals suffering from a range of substance use disorders.^[69] In a randomized clinical trial, 160 adults with any substance use disorder received either treatment plus computer-based CRT or treatment without CRT; these individuals were followed for one year after treatment in a residential program.^[69] Those that had received the CRT showed higher scores on neuropsychological tasks during treatment, though these improvements did not persist at the 12-month follow-up evaluation.^[69] Individuals with CRT also showed significantly greater engagement in treatment, commitment to therapy, and a persistent reduction in substance use frequency and addiction severity, demonstrating that CRT has wide-reaching positive effects even above cognitive enhancement.^[69]

CRT has additionally been used in populations with one specific substance use disorder such as alcohol dependence.^[70] A study of 41 individuals with alcohol dependence revealed patients who had received treatment plus computer-based CRT had greater improvements in working memory, delayed recall memory, and attention as compared to patients who received treatment without CRT.^[70] In addition, CRT patients demonstrated endorsed fewer psychological symptoms and impairment post-treatment than non-CRT patients, particularly noting less compulsion-based craving.^[70] The effects of CRT on improving cognition in individuals with alcohol dependence has been demonstrated in several other studies using attentional retraining methods.^[66]

Although this field is reportedly in its infancy with limited data available, CRT has been proposed as a potentially effective and efficacious treatment for several other substance use disorders including stimulant abuse.^[61]

Cognitive deficits have long been associated with Attention-Deficit/Hyperactivity disorder (ADHD), particularly within executive function, inhibitory control, organizational skills, and divided, selective, and sustained attention.^[71] Among adults, these deficits have been successfully targeted by CRT that included coaches and homework; as compared to wait-list controls, 22 adults exhibited improved symptomatology (including reduced anger) and organizational skills that persisted to a one-year follow-up evaluation.^[72]

Although there is a large literature on CRT treatment of adults with ADHD, there is evidence of success among children as well. In fact, there appears to be more support for the transferring of improvement between the targeted ability and other cognitive areas among children as compared to adults.^[11] One review highlighted that children with ADHD had successful reductions in ADHD symptoms and improved academic skills following CRT, as well as improved working memory and attention.^[19] The use of more varied CRT approaches, such as one involving movement-based visual and auditory tasks, have led to preschool children with high-risk ADHD symptoms showing improved selective attention and executive control as compared to controls.^[73] Therefore, even diverse, sensorimotor CRT programs can successfully address impairments related to ADHD symptoms, though this study was limited by a relatively small sample.^[73]

CRT has shown efficacy for improving cognition among a range of other disorders and conditions, though with more limited evidence than those addressed above. Preliminary evidence via a pilot study of two adults with borderline personality disorder, showed that 40 sessions of biweekly CRT improved verbal working memory, processing speed, planning, self-esteem, and performance in everyday tasks like multi-tasking.^[74] In one study of children with language-based learning disabilities, post-CRT improvements in auditory perception were observed.^[19] Similarly, attention training reportedly decreased impulsive behaviors and the frequency of tics and improved quality of life among children with Tourette Syndrome.^[19]

Non-psychiatric medical conditions such as cancer can also result in cognitive impairment.^[75] CRT appears to improve performance on attentional tasks among cohorts of childhood cancer survivors who have attentional difficulties, but the evidence remains inconsistent regarding generalized improvement in academic achievement.^[75][76]

CRT has also been applied to disorders of aging, such as Alzheimer’s Disease and dementia. A review of the literature revealed several computer-based CRT programs modified for Alzheimer’s have led to a wide range of documented improvements in cognition, working memory, depressive symptoms, and executive functioning.^[77] Additionally, the combination of one-on-one CRT with motor movements had increased positive effects over and above those caused by psychosocial support alone, for example.^[77] However, other reviews were unable to find positive effects of CRT on alleviating memory deficits among those with vascular dementia or Alzheimer’s Disease due to poor quality of the randomized controlled trials, again highlighting inconsistencies in this early line of research.^[78][79] However, computerized CRT has been shown to be preliminarily beneficial for other aspects of aging, such as for improving gait velocity and multitasking while walking (i.e., walking and talking) among elderly individuals.^[80]

Cognitive rehabilitation, a more comprehensive cognitive enhancement program that takes place in a rehabilitation setting, has also been substantially shown (i.e., via reviews and meta-analyses) to aid in cognitive disability brought on by brain injuries such as traumatic brain injuries and strokes.^[81]

CRT was not necessarily developed as a tool to be used in place of pharmacological, cognitive behavioral therapy (CBT), or other interventions, though some research has shown it to be as effective as (or more effective than) CBT, for example, in reducing schizophrenia symptoms and minimizing safety concerns.^[82][83] Instead, a multimodal approach may in fact be ideal, in which CRT is used in addition to those other methodologies in order to best combat cognitive decline.^{[84][85][86][87]} For example, CRT combined with trauma therapy, psychosocial and vocational rehabilitation, or CBT may be most effective for treating severe mental illness and creating lasting cognitive improvement,^{[23][84][85][86][87]} while aspects of CRT incorporated into school curricula may help children with attentional or language-based difficulties.^[19] Similarly, flexible CRT-related strategies for helping with attention, memory, and problem-solving can be directly applied to skills-based work in psychosocial therapies for a range of psychiatric conditions.^[88] In particular, CRT combined with therapy (namely, when therapists are aware of the training) has been suggested to facilitate discussions of applying training exercises to daily lives, increasing the day-to-day relevance of this treatment.^[47]

Researchers caution that assessing salient cognitive changes from a research framework (e.g., using statistical significance) does not always translate into clinical significance.^[2] Specifically, the use of neuropsychological tests that examine larger cognitive indices may make it difficult to assess subtle changes in cognition.^[2] This often leads to modest group-wide treatment effect sizes reported in meta-analyses that may underestimate the important and practical changes that may have taken place within the individual’s daily life.^[2] Additionally, the variation in outcome measures used by each study makes comparisons between them challenging, limiting the generalizability of results.^[23] However, multisite studies are also beginning to take form to help establish uniformity, and confirm neurocognitive improvements in SZ patients following CRT.^[24] Another limitation is that while CRT appears to have great promise for improving cognitive deficits, consensus suggests that there may be limited real-life, day-to-day applicability (e.g., remembering a grocery list better).^[58] Therefore, more research is deemed necessary to further assess applicability and practicality for individuals.^[89]

Cognitive remediation therapy (CRT), also referred to as cognitive rehabilitation or cognitive enhancement,^[1] has been defined by the Cognitive Remediation Experts Workshop as a ″behavioral-training based intervention that aims to improve cognitive processes (attention, memory, executive function, social cognition, or metacognition) with the goal of durability and generalization″.^[2] CRT also aims to affect the domains of working memory, cognitive flexibility, and problem solving, ultimately intending to improve functioning in everyday life. Cognitive remediation is used to treat the deficits in neurocognitive abilities that may have resulted from a range of neurological and psychiatric disorders or from other brain injuries. CRT aims to take advantage of the brain’s plasticity, or its ability to change, in order to improve deficits in abilities.^[2]

The theory of applying methods to improve cognitive deficits has been discussed as early as 1896.^[3] However, the earliest documented examples of CRT date back to World War I, during which time soldiers returning from war evidenced brain injuries necessitating assessment and rehabilitation.^[4][5] Clinics treating these soldiers developed internationally in Germany, Great Britain, and Russia,^[4][5] with the Soviet neuropsychologist Alexander Luria providing much information about injury-related brain dysfunction.^[6] In particular, Luria assessed the current functioning of soldiers on a neurosurgical unit, investigated medications that could improve memory skills, and identified the functions of various brain regions.^[4]

Within the United States, the rehabilitation field was developing with psychologists such as Shepherd Franz commenting on related “reeducation” techniques.^[4][5] Others, such as Kurt Goldstein continued studying soldiers who had sustained brain injuries, noting their restrictions and suggesting psychotherapy treatments as remedies.^[6] Later advances in neurocognition and cognitive psychology in the 1960s led to the modern remediation methods used today,^[4] with the burgeoning field of neuropsychology and its testing tools aiding in the assessment of cognitive deficits needing intervention.^[6] For example, the earliest known study on CRT in psychotic patients dates back to 1973.^[7] The additional advances in modern technology throughout the 1980s and 1990s, in particular, the development of computers and video gaming systems (e.g., Atari) allowed for the introduction of educational and rehabilitation software that could be used with individuals who had experienced traumatic brain injuries.^[8] Although current CRT iterations were developed in the early 1990s, the accepted, formalized definition above was not ratified until 2010 by the Cognitive Remediation Experts Workshop.^[2]

One CRT technique is to teach individuals "errorless learning," or learning to complete tasks in structured situations that minimize the number of errors that can be made.^[2] This can be accomplished by initially presenting a task very slowly and then increasing the speed, or by breaking down a task into smaller, simpler steps.^[2] Other technique are "self-monitoring," for which the individual is taught to develop routines for remembering instructions and completing the task, and "scaffolding," where assistance is provided based on the person’s level of competency and is altered as the skill grows.^[2] CRT can focus on extended practice on a single task, or can involve multiple tasks and strategies intended to improve functioning on a particular skill.^[2] Cognitive training is provided either though computer-based tasks or pencil-and-paper activities, during which either an examiner or a computer-based program will provide feedback and alter task difficulty.^[9]

In order to determine which tasks should be used to address deficits in certain cognitive abilities, researchers rely on several assumptions of CRT, which one group deemed the "higher-order assumption," the "central-deficit assumption," and the "task-purity assumption".^[10] The higher-order assumption refers to the idea that certain functions are targeted for treatment because they are thought to influence several downstream cognitive processes; therefore, improvement in this function would lead to improvement in many others.^[10] The central-deficit assumption states that the deficit targeted by CRT must be one that is centrally related to the disorder in question.^[10] Lastly, that the training exercise is known to target the impaired ability.^[10] Although these assumptions are often employed by researchers, the research highlights some theoretical weakness regarding the validity of them.^[10]

CRT aims to improve cognition to a noticeable, long lasting extent in one of three main ways: helping to regain lost skills, aiding in the acquiring of new skills, or improving global functioning.^[2] It does so by affecting and altering existing neural pathways in the brain.^[11] In a typical brain, regions communicate with one another through connections established by neural synapses.^[12] These highly organized connections^[13] become damaged or atypical due to various psychiatric/neurological disorders,^[14] and can cause observable cognitive deficits associated with those disorders. However, due to the brain’s plasticity, or the ability of experience to modify brain structures and corresponding function, neural circuitry can be altered in many ways to restore such deficits.^[15][16] By providing an enriched environment, CRT has been shown to facilitate such neural plasticity and promote recovery.^[11]

For example, a recent review of the neural substrates altered by CRT in schizophrenia (SZ) patients showed significant post-CRT increases in activation within frontal brain regions such as the prefrontal cortex, as well as in changes in limbic, parietal, temporal, and [[parahippocampal gyrus|parahippocampal] areas using functional magnetic resonance imaging (fMRI) techniques.^[9] Structural MRI techniques have revealed changes in gray matter volume in medial temporal areas of SZ patients (e.g., amygdala, hippocampus, anterior cingulate cortex) following CRT, namely that CRT appears to have neuroprotective effects of reducing gray matter loss in those regions or even facilitating localized increases in gray matter volume.^[9] Changes to white matter organization have also been reported via diffusion tensor imaging techniques.^[9]

These neural changes are then measured by comparing pre-CRT performance on standardized neuropsychological tests to performance on these tests following CRT, with the goal to find improvements in the areas examined.^[2][17] Indeed, observed neural changes often correlate with such enhancements in neurocognitive performance.^[9]

Overall, CRT has been reported to have small to moderate effects on global cognition, social cognition, verbal working memory, and daily functioning that at times appear relatively long-lasting.^[9] However, some differences within individual psychiatric conditions exist.

The largest CRT literature on severe mental illness exists among the schizophrenia (SZ) cohort,^[18] in part due to the inability of other existing treatments to address the persistent declines in cognition often observed in psychosis-spectrum disorders.^[19] Computerized CRT has been shown to increase attention, processing speed, verbal memory and working memory with small effect sizes, with the largest (medium) effect size observed in the improvement in social cognition; results were independent of whether or not these domains were specifically targeted by CRT tasks.^[20] Treatment duration, remediation approach, and training delivery method (e.g., computerized or not) were reported not have an effect on cognitive changes, but functioning outcome appears most affected by the increased clinical stability of patients and the conjunction of CRT with other treatment options.^[21] The benefits of CRT have also been demonstrated in disorders related to SZ, such as schizoaffective disorder.^[22]

There is a large body of research addressing CRT as a treatment for the cognitive deficits associated with anorexia nervosa (AN), an eating disorder, such as cognitive inflexibility (e.g., the ability to switch between strategies and multitask), and extreme detail-oriented thinking that leads to restrictive eating.^[23][24] CRT for AN, the creation of which has been credited to Tchanturia and Davies,^[23] has been described as broadly targeting cognitive style (thought process) rather than focusing on the more specific symptoms of emotions, weight, or eating (thought content).^[24] CRT for AN has also been reported to have low drop-out rates, suggesting that this is a promising treatment approach among a cohort that usually has difficulty engaging in therapy.^[24]

Mood disorders such as Major Depressive Disorder (MDD) have been associated with cognitive impairment in a wide range of executive function and neuropsychological tasks such as those assessing attention, memory, working memory, and psychomotor skills.^[25] Similar deficits in processing speed, attention, memory, and executive functioning have been reported in bipolar disorder as well.^[26] There is some effect of diagnostic variability, with greater cognitive deficits accompanying bipolar disorder(BP) than unipolar depression (MDD), and mood disorders with psychotic features showing the greatest impairments.^[25] Some of the cognitive dysfunction appears to persist even after clinical symptoms have remitted,^[25] necessitating the use of tools such as CRT to combat these effects.

A recent review of CRT for mood disorders revealed improvements in depressive symptoms and psychosocial functioning, as well as increased occupational functioning that correlated with better executive functioning, following remediation in individuals with BP.^[26] However, people with more severe cognitive functioning prior to treatment appeared to benefit less from CRT, suggesting that CRT may need to be more individualized for those with greater impairments.^[26] Given the paucity of current research addressing the benefits of CRT for BP, replication of such findings among independent samples is recommended.^[26]

Much more work has been done reviewing the effects of CRT on individuals with depression though with inconsistent findings reported; increases in executive functioning and decreases in depressive symptoms and rumination among adults with MDD have been suggested after remediation intervention.^[26] Given these inconsistencies in the literature, a recent review suggested that sample sizes have been too small to be conclusive in their findings, but that additional research using more well-defined criteria is warranted to continue to assess the impact of CRT on mood disorders.^[27]

The negative effects of substance use on cognition and brain development have been well documented especially in the domains of memory and attention,^[28][29][30] with particular detrimental effects observed in adolescents.^[31] The effects of CRT on improving cognition in individuals with alcohol dependence has been demonstrated in several studies using attentional retraining methods,^[30] Although this field is reportedly in its infancy with limited data available, CRT has been proposed as a potentially effective and efficacious treatment for several other substance use disorders including stimulant abuse.^[28]

Cognitive deficits have long been associated with Attention-Deficit/Hyperactivity disorder (ADHD), particularly within executive function, inhibitory control, organizational skills, and divided, selective, and sustained attention.^[32] Although there is a large literature on CRT treatment of adults with ADHD, there is evidence of success among children as well. In fact, there appears to be more support for the transferring of improvement between the targeted ability and other cognitive areas among children as compared to adults.^[33] Children with ADHD have had successful reductions in ADHD symptoms and improved academic skills following CRT, as well as improved working memory and attention.^[16]

CRT has shown efficacy for improving cognition among a range of other disorders and conditions. Children with language-based learning disabilities have shown post-CRT improvements in auditory perception were observed,^[16] while attention training has decreased impulsive behaviors and the frequency of tics and improved quality of life among children with Tourette Syndrome.^[16] CRT has also been applied to disorders of aging, such as Alzheimer’s Disease and dementia. Several computer-based CRT programs modified for Alzheimer’s have led to a wide range of documented improvements in cognition, working memory, depressive symptoms, and executive functioning according to a recent review.^[34] Additionally, the combination of one-on-one CRT with motor movements increases positive effects over and above those caused by psychosocial support alone, for example.^[34] However, other reviews were unable to find positive effects of CRT on alleviating memory deficits among those with vascular dementia or Alzheimer’s Disease due to poor quality of the randomized controlled trials, highlighting inconsistencies in this line of research.^[35]

Cognitive rehabilitation, a more comprehensive cognitive enhancement program that takes place in a rehabilitation setting, has also been substantially shown (i.e., via reviews and meta-analyses) to aid in cognitive disability brought on by brain injuries such as traumatic brain injuries and strokes.^[36]

CRT was not necessarily developed as a tool to be used in place of pharmacological, cognitive behavioral therapy (CBT), or other interventions. Instead, a multimodal approach may in fact be ideal, in which CRT is used in addition to those other methodologies in order to best combat cognitive decline.^[37][38] For example, CRT combined with trauma therapy, psychosocial and vocational rehabilitation, or CBT may be most effective for treating severe mental illness and creating lasting cognitive improvement,^[38][37][18] while aspects of CRT incorporated into school curricula may help children with attentional or language-based difficulties.^[16]

Researchers caution that assessing salient cognitive changes from a research framework (e.g., using statistical significance) does not always translate into clinical significance.^[2]. Specifically, the use of neuropsychological tests that examine larger cognitive indices may make it difficult to assess subtle changes in cognition.^[2] This often leads to modest group-wide treatment effect sizes reported in meta-analyses that may underestimate the important and practical changes that may have taken place within the individual’s daily life.^[2] Additionally, the variation in outcome measures used by each study makes comparisons between them challenging, limiting the generalizability of results.^[18] Therefore, more research is deemed necessary to further assess applicability and practicality for individuals.^[39]

CRT, or the more broad [[brain fitness|brain training], has been shown to boost general cognitive skills within healthy or typically-developing populations in addition to psychiatric ones^[16] such as through programs like BrainHQ by Posit Science or Lumosity. Literature reviews demonstrate that such training may be beneficial for children, adults, and elderly individuals alike.^[16] Additionally, the category of brain training has extended to encompass areas outside of traditional CRT, such as music-based training, meditation, and physical exercise, which have all been shown to positively impact and enhance cognitive functioning.^[16]