The introduction of computerized neurocognitive batteries offers more precise response time measurements, more narrowly defined behavioral domain measures, increased accuracy of stimulus timing presentation, shorter assessment times, standardized administration, automatic scoring, convenient data storage and easy transport for bedside or home access. While there are some technical and theoretical concerns raised about computerized assessments (7
), previous work has reported favorable reliability and construct validity of using computerized measures in younger cohorts of adults with schizophrenia. Yet, the performance of older patients with schizophrenia on computerized measures has not been unexamined. Using one of the largest samples of older schizophrenia patients examined to date, we found that 94% of the younger participants and 91% of the older participants provided “good” data quality when completing a 1–2 hour long research based computerized neurocognitive battery. Qualitatively, the main difficulties in older and younger groups revolved around incomplete practice trials of some tests due to concentration difficulties or low effort and mouse or keyboard handling difficulties. But these difficulties were only found in 9% of the older cohort and 6% of the younger cohort. Overall, this supports the feasibility of using computerized measures to assess cognition across the lifespan in schizophrenia. It may also allay concerns about older patients’ unfamiliarity or discomfort with computers and potential poor tolerability of computerized assessments.
The comprehensive neurocognitive assessment also allowed further clarification of the relationship between aging and cognitive performance in schizophrenia. Our data indicated that there was significantly reduced accuracy, speed and efficiency for both younger and older schizophrenia patients when compared to their age-matched healthy comparison groups across the neurocognitive domains of the CNB. This replicates robust observations of large and generalized deficits in younger schizophrenia patients’ performance on computerized neurocognitive tasks (10
) and extends these findings to later in the lifespan. This finding is consistent with the traditional paper-pencil based literature that has also shown large global and domain specific neuropsychological dysfunction in older individuals with schizophrenia (28
Further examination of age-stratified effects did not reveal significant differences in accuracy, response time or efficiency scores in the older group, aged 45–60 and those over 60 years of age. However, it is worth noting that while younger patients and those aged 45–59 performed significantly worse than their respective healthy comparison groups on all domains, in the oldest group of 60+ individuals, patients were less accurate than comparison subjects only for attention and emotion processing and less efficient in attention, working memory and spatial memory. In the remaining domains, the gap between patients and comparison groups was small and statistically non-significant. This indicates that with the noted exceptions, in the very old group there is either a normative decline in abstraction, facial memory, verbal memory, language and spatial processing or a relative improvement in patients’ performance on these domains. Overall however, there appears to be stability of neurocognitive impairment across the lifetime in schizophrenia, without support for a hypothesis of widespread cognitive degeneration emerging later in life in patients with schizophrenia.
In addition to being one of the few domains that showed persistent impairment in accuracy and efficiency in patients relative to their HC group, even in the 60+ age group, the domain for attention was further notable since it showed greater reductions in both accuracy and response time, hence efficiency, for older patients relative to younger ones. Deficits in attention are often considered to be central features of the clinical presentation of schizophrenia and have garnered support as candidate endophenotypes (11
). In our battery attention is assessed using the Penn Continuous Performance Test, a measure of visual sustained attention. CPT impairments have been shown in first episode patients with schizophrenia followed longitudinally even in clinically remitted states (43
). Much of the prior work with older cohorts has focused on measures of brief attention like the digit span (44
). Consistent with our findings, one prior study with older patients used auditory CPT errors as an index for sustained attention and found similar age-related decline in patients and comparison subjects (47
). The apparent age related decline in this domain might reflect inefficiency of frontal networks for sustained attention. Some have suggested that the mechanism that causes cognitive aging is a general reduction in attentional resources (48
) and future investigation is needed to examine whether schizophrenia is associated with greater decomposition of networks recruited in sustained attention compared to other brain systems.
The use of a computerized battery further permitted the evaluation of individual differences in strategy that are relevant for speed–accuracy tradeoffs (49
). Efficiency of performance, which reflected the degree to which participants effectively slowed their response time in order to maintain accuracy levels, provided uniquely valuable information about testing strategies. For instance, we found that compared to younger patients, older patients’ lower efficiency in the working memory domain reflected reduced speed, but not accuracy. On the whole, older patients’ performed at similar accuracy levels as younger patients across the neurocognitive domains of the CNB. Consistent with this finding, working memory accuracy has been stable in non-institutionalized outpatients with schizophrenia across the life span (50
). A functional magnetic resonance imaging investigation of middle-aged and older patients with schizophrenia showed that even though accuracy was near normal on a spatial working memory task when the processing demands of the task were within their performance capacity, patients demonstrated an aberrant pattern of brain response (51
). Thus, our observation of longer response times to complete working memory tasks by older cohorts may reflect inadequacy in the neural networks subserving working memory functions in this older group. This inefficiency appears to extend late into life, as evident in persistent impairment demonstrated by the 60+ patients.
Another domain where older patients showed a differential style of responding compared to younger patients was in emotional processing. Since emotion processing is typically not assessed in traditional neuropsychological evaluations, this is a domain that has been neglected in studies of elderly schizophrenia patients. Yet since social cognitive processes such as emotional processing act as key mediators between core (nonsocial) cognition and functional outcome (52
), it is an area requiring further attention. In our study, surprisingly older patients were relatively quicker than younger patients when identifying and discriminating facial emotions. Previous work in younger cohorts has shown that impaired emotional functioning is a prominent feature of schizophrenia and is highly heritable (12
). The socio-emotional selectivity theory posits that aging is associated with directed attention towards emotionally meaningful situations and goals due to perceived limitations on time (54
). This could account for why older patients were more likely to provide rapid responses when making decisions about the emotions on faces. Yet, structural and functional impairments in the neural circuitry underlying emotion processing have been robustly noted in patients (55
) and likely account for the observed stable impairments in accuracy and overall inefficiency of facial emotion recognition.
While our data do not support the hypothesis that there is a global neurodegenerative course associated with patients with lower levels of functional deficits at baseline (57
), long-stay institutionalized patients were not the focus of our investigation. The current study was also limited by the presence of some outliers in our data who may have been representative of more impaired individuals. We attempted to account for these outliers by conducting a sensitivity analysis, and found no remarkable differences when outliers were excluded, truncated or included. Another limitation of our study lies in the variability for the number of subjects who completed various CNB tasks within a cognitive domain. Since this analysis was conducted with data from different projects, the tasks included in a battery varied slightly across projects. This introduces some inconsistency in the composition of the cognitive domains being assessed, yet the cognitive constructs (e.g. “verbal memory”) remained consistent in our analysis. Also because the ensuing length of the batteries across projects varied slightly (from 1–2 hours) we cannot account for differential rates of fatigue and task order effects. We did however examine the impact of project in our analyses and found that it was not a significant contributor in the models. Finally, the groups in our sample were unequally matched for parental education. While parental education contributed to the overall variance in the models, effect sizes were small and cannot account for the findings.
These limitations notwithstanding, our findings indicated that older patients with schizophrenia were able to tolerate a computerized neurocognitive battery. Their performance was also consistent with a large body of prior research indicating stability of generalized neurocognitive dysfunction in patients diagnosed with schizophrenia across the lifespan. We replicated and further extended this line of work in a very large sample to show that sensitive computerized measures can provide additional information about speed-accuracy trade-off strategies used by older patients when challenged with cognitive tasks. For instance, speed of emotional processing abilities improved with age in schizophrenia, although accuracy with which emotions were identified and discriminated remained impaired throughout the lifespan. Conversely, inefficiency in working memory functions in older patients was driven by longer response times and not reduced accuracy. On a sustained attention task, older patients were less accurate and slower than younger patients. This may reflect more rapid deterioration with aging in schizophrenia of some frontal system networks involving attention and working memory, but more work is needed to further delineate the putative brain regions involved. Overall, there is stable and generalized neurocognitive dysfunction across the lifespan in schizophrenia, albeit with improvement in some domains after age 60.