There is considerable evidence of cognitive impairment post COVID-19, especially in individuals with long-COVID symptoms, but limited research objectively evaluating whether such impairment attenuates or resolves over time, especially in young and middle-aged adults.

Follow-up assessments (T2) of cognitive function (processing speed, attention, working memory, executive function, memory) and mental health were conducted in 138 adults (18–69 years) who had been assessed 6 months earlier (T1). Of these, 88 had a confirmed history of COVID-19 at T1 assessment (≥20 days post-diagnosis) and were also followed-up on COVID-19-related symptoms (acute and long-COVID); 50 adults had no known COVID-19 history at any point up to their T2 assessment.

From T1 to T2, a trend-level improvement occurred in intra-individual variability in processing speed in the COVID, relative to the non-COVID group. However, longer response/task completion times persisted in participants with COVID-19-related hospitalisation relative to those without COVID-19-related hospitalisation and non-COVID controls. There was a significant reduction in long-COVID symptom load, which correlated with improved executive function in non-hospitalised COVID-19 participants. The COVID group continued to self-report poorer mental health, irrespective of hospitalisation history, relative to non-COVID group.

Although some cognitive improvement has occurred over a 6-month period in young and middle-aged COVID-19 survivors, cognitive impairment persists in those with a history of COVID-19-related hospitalisation and/or long-COVID symptoms. Continuous follow-up assessments are required to determine whether cognitive function improves or possibly worsens, over time in hospitalised and long-COVID participants.

Executive functioning (EF) is known to be associated with performance of instrumental activities of daily living (IADLs). However, prior research has found that the degree to which EF fluctuates was more predictive of self-reported cognitive and IADL lapses than was average EF performance. One source of such EF fluctuations is engagement in an emotion regulation strategy known as expressive suppression (ES). Importantly, ES has also been shown to relate to IADL performance, presumably due to its impact on EF. However, past research is limited due to assessing IADLs only in the laboratory or via self-report. The present study examined (a) the association of daily EF and ES fluctuations with performance of actual IADL tasks in participants’ homes, and (b) whether any significant association between ES fluctuations and daily IADLs would be mediated by daily EF variability.

Participants were 52 older adults aged 60 to 95. Over the course of 18 days while at home, participants completed daily IADL tasks as well as daily measures of EF and ES via ecological momentary assessment.

Contrary to our hypothesis, average EF across days predicted at-home IADLs above and beyond daily EF variability, which itself was also predictive. ES variability also predicted daily IADLs, and this association was fully mediated by average daily EF.

Daily fluctuations in ES appear to have a deleterious impact on performance of IADLs at home, likely due to the impact of such fluctuations on EF, although the average level of EF capacity is also important.

Increased intra-subject reaction time variability (RT-ISV) as coarsely measured by the standard deviation (RT-SD) has been associated with many forms of psychopathology. Low-frequency RT fluctuations, which have been associated with intrinsic brain rhythms occurring approximately every 15–40 s, have been shown to add unique information for ADHD. In this study, we investigated whether these fluctuations also relate to attentional problems in the general population, and contribute to the two major domains of psychopathology: externalizing and internalizing problems.

RT was monitored throughout a self-paced sustained attention task (duration: 9.1 ± 1.2 min) in a Dutch population cohort of young adults (n = 1455, mean age: 19.0 ± 0.6 years, 55.1% girls). To characterize temporal fluctuations in RT, we performed direct Fourier Transform on externally validated frequency bands based on frequency ranges of neuronal oscillations: Slow-5 (0.010–0.027 Hz), Slow-4 (0.027–0.073 Hz), and three additional higher frequency bands. Relative magnitude of Slow-4 fluctuations was the primary predictor in regression models for attentional, internalizing and externalizing problems (measured by the Adult Self-Report questionnaire). Additionally, stepwise regression models were created to investigate (a) whether Slow-4 significantly improved the prediction of problem behaviors beyond the RT-SD and (b) whether the other frequency bands provided important additional information.

The magnitude of Slow-4 fluctuations significantly predicted attentional and externalizing problems and even improved model fit after modeling RT-SD first (R2 change = 0.6%, P < .01). Subsequently, adding Slow-5 explained additional variance for externalizing problems (R2 change = 0.4%, P < .05). For internalizing problems, only RT-SD made a significant contribution to the regression model (R2 = 0.5%, P < .01), that is, none of the frequency bands provided additional information.

Low-frequency RT fluctuations have added predictive value for attentional and externalizing, but not internalizing problems beyond global differences in variability. This study extends previous findings in clinical samples of children with ADHD to adolescents from the general population and demonstrates that deconstructing RT-ISV into temporal components can provide more distinctive information for different domains of psychopathology.

Intra-individual variability (IIV) and the change of attentional functions have been reported to be susceptible to both healthy ageing and pathological ageing. The current study aimed to evaluate the IIV of attention and the age-related effect on alerting, orienting, and executive control in cognitively healthy older adults.

We evaluated 145 Chinese older adults (age range of 65–80 years, mean age of 72.41 years) with a comprehensive neuropsychological battery and the Attention network test (ANT). A two-step strategy of analytical methods was used: Firstly, the IIV of older adults was evaluated by the intraindividual coefficient of variation of reaction time (ICV-RT). The correlation between ICV-RT and age was used to evaluate the necessity of subgrouping. Further, the comparisons of ANT performance among three age groups were performed with processing speed adjusted.

Person's correlation revealed significant positive correlations between age and IIV (r = 0.185, p = 0.032), age and executive control (r = 0.253, p = 0.003). Furthermore, one-way ANOVA comparisons among three age groups revealed a significant age-related disturbance on executive control (F = 4.55, p = 0.01), in which oldest group (group with age >75 years) showed less efficient executive control than young-old (group with age 65–70 years) (Conventional score, p = 0.012; Ratio score, p = 0.020).

Advancing age has an effect on both IIV and executive attention in cognitively healthy older adults, suggesting that the disturbance of executive attention is a sensitive indicator to reflect healthy ageing. Its significance to predict further deterioration should be carefully evaluated with prospective studies.

Increased intra-individual variability (IIV) in reaction time (RT) across various tasks is one ubiquitous neuropsychological finding in attention deficit hyperactivity disorder (ADHD). However, neurobiological underpinnings of IIV in individuals with ADHD have not yet been fully delineated. The ex-Gaussian distribution has been proved to capture IIV in RT. The authors explored the three parameters [μ (mu), σ (sigma), τ (tau)] of an ex-Gaussian RT distribution derived from the Conners' continuous performance test (CCPT) and their correlations with the microstructural integrity of the frontostriatal–caudate tracts and the cingulum bundles.

We assessed 28 youths with ADHD (8–17 years; 25 males) and 28 age-, sex-, IQ- and handedness-matched typically developing (TD) youths using the CCPT, Wechsler Intelligence Scale for Children, 3rd edition and magnetic resonance imaging (MRI). Microstructural integrity, indexed by generalized fractional anisotropy (GFA), was measured by diffusion spectrum imaging tractrography on a 3-T MRI system.

Youths with ADHD had larger σ (s.d. of Gaussian distribution) and τ (mean of exponential distribution) and reduced GFA in four bilateral frontostriatal tracts. With increased inter-stimulus intervals of CCPT, the magnitude of greater τ in ADHD than TD increased. In ADHD youths, the cingulum bundles and frontostriatal integrity were associated with three ex-Gaussian parameters and with μ (mean of Gaussian distribution) and τ, respectively; while only frontostriatal GFA was associated with μ and τ in TD youths.

Our findings suggest the crucial role of the integrity of the cingulum bundles in accounting for IIV in ADHD. Involvement of different brain systems in mediating IIV may relate to a distinctive pathophysiological processing and/or adaptive compensatory mechanism.

Few studies have examined the short-term course of cognitive impairments in bipolar disorder (BD). Key questions are whether trajectories in symptoms covary with cognitive function and whether BD is associated with increased intra-individual variability in cognitive abilities.

Forty-two out-patients with BD and 49 normal comparison (NC) subjects were administered a battery of neuropsychological tests at baseline, 6, 12 and 26 weeks, along with concurrent ratings of depressive and manic symptom severity. Mixed-effects regressions were used to model relationships between time, diagnosis and symptom severity on composite cognitive performance. Within-person variance in cognitive functioning across time was calculated for each subject.

BD patients had significantly worse performance in cognitive ability across time points, but both groups showed significant improvement in cognitive performance over repeated assessments (consistent with expected practice effects). BD was associated with significantly greater intra-individual variability in cognitive ability than NCs; within-person variation was negatively related to baseline cognitive ability in BD but not NC subjects. Changes in affective symptoms over time did not predict changes in cognitive ability.

Moderate changes in affective symptoms did not covary with cognitive ability in BD. The finding of elevated intra-individual variability in BD may reduce capacity to estimate trajectories of cognitive ability in observational and treatment studies.