Task-Dependent Oscillatory Brain Activity During Oculomotor Delayed Response Task

This study used three Oculomotor Delayed Response (ODR) tasks to investigate the unique cognitive demands during the delay period. Changes in alpha power were used to index cognitive efforts during the delay period. Continuous EEGs from 25 healthy young adults (18-34 years) were recorded using dense electrode array. The data was analyzed by 6-cycle Morlet wavelet decompositions in the frequency range of 2-30 Hz to create time- frequency decompositions for four midline electrode sites. The 99% confidence intervals using the bootstrapped 20% trimmed mean of the 10 Hz frequency were used to examine the differences among conditions. Compared to two Memory conditions (Match and Non-Match), Control condition yielded significant differences in all frequencies over the entire trial period, suggesting a cognitive state difference. Compared to Match condition, the Non–Match condition had lower alpha activity during the delay period at each midline electrode site reflecting the higher cognitive effort required.

Genetic sources of covariation among P3(00) and online performance variables in a delayed-response working memory task

Genetic and environmental sources of covariation among the P3(00) and online performance elicited in a delayed-response working memory task, and psychometric IQ assessed by the multidimensional aptitude battery, were examined in an adolescent twin sample. An association between frontal P3 latency and task performance (phenotypic r = -0.33; genotypic r = -0.49) was indicated, with genes (i.e. twin status) accounting for a large part of the covariation ( > 70%). In contrast, genes influencing P3 amplitude mediated only a small part (2%) of the total genetic variation in task performance. While task performance mediated 15% of the total genetic variation in IQ (phenotypic r = 0.22; genotypic r = 0.39) there was no association between P3 latency and IQ or P3 amplitude with IQ. The findings provide some insight into the inter-relationships among psychophysiological, performance and psychometric measures of cognitive ability, and provide support for a levels-of-processing genetic model of cognition where genes act on specific sub-components of cognitive processes.

Electrophysiology of Oculomotor Delayed Response Tasks: A Model for the Maturation of Visual-Spatial Working Memory Networks

In the literature, persistent neural activity over frontal and parietal areas during the delay period of oculomotor delayed response (ODR) tasks has been interpreted as an active representation of task relevant information and response preparation. Following a recent ERP study (Tekok-Kilic, Tays, & Tkach, 2011 ) that reported task related slow wave differences over frontal and parietal sites during the delay periods of three ODR tasks, the present investigation explored developmental differences in young adults and adolescents during the same ODR tasks using 128-channel dense electrode array methodology and source localization. This exploratory study showed that neural functioning underlying visual-spatial WM differed between age groups in the Match condition. More specifically, this difference is localized anteriorly during the late delay period. Given the protracted maturation of the frontal lobes, the observed variation at the frontal site may indicate that adolescents and young adults may recruit frontal-parietal resources differently.

Effects of memory load and distraction on performance and event-related slow potentials in a visuospatial working memory task

Brain electrical activity related to working memory was recorded at 15 scalp electrodes during a visuospatial delayed response task. Participants (N = 18) touched the remembered position of a target on a computer screen after either a 1 or 8 sec delay. These memory trials were compared to sensory trials in which the target remained present throughout the delay and response periods. Distracter stimuli identical to the target were briefly presented during the delay on 30% of trials. Responses were less accurate in memory than sensory trials, especially after the long delay. During the delay slow potentials developed that were significantly more negative in memory than sensory trials. The difference between memory and sensory trials was greater at anterior than posterior electrodes. On trials with distracters, the slow potentials generated by memory trials showed further enhancement of negativity whereas there were minimal effects on accuracy of performance. The results provide evidence that engagement of visuospatial working memory generates slow wave negativity with a timing and distribution consistent with frontal activation. Enhanced brain activity associated with working memory is required to maintain performance in the presence of distraction. © 1997 by the Massachusetts Institute of Technology

Delayed response and lack of habituation in plasma interleukin-6 to acute mental stress in men

Acute mental stress induces a significant increase in plasma interleukin (IL)-6 levels as a possible mechanism for how psychological stress might contribute to atherosclerosis. We investigated whether the IL-6 response would habituate in response to a repetitively applied mental stressor and whether cortisol reactivity would show a relationship with IL-6 reactivity. Study participants were 21 reasonably healthy men (mean age 46+/-7 years) who underwent the Trier Social Stress Test (combination of a 3-min preparation, 5-min speech, and 5-min mental arithmetic) three times with an interval of 1 week. Plasma IL-6 and free salivary cortisol were measured immediately before and after stress, and at 45 and 105 min of recovery from stress. Cortisol samples were also obtained 15 and 30 min after stress. Compared to non-stressed controls, IL-6 significantly increased between rest and 45 min post-stress (p=.022) and between rest and 105 min post-stress (p=.001). Peak cortisol (p=.034) and systolic blood pressure (p=.009) responses to stress both habituated between weeks one and three. No adaptation occurred in diastolic blood pressure, heart rate, and IL-6 responses to stress. The areas under the curve integrating the stress-induced changes in cortisol and IL-6 reactivity were negatively correlated at visit three (r=-.54, p=.011), but not at visit one. The IL-6 response to acute mental stress occurs delayed and shows no adaptation to repeated moderate mental stress. The hypothalamus-pituitary-adrenal axis may attenuate stress reactivity of IL-6. The lack of habituation in IL-6 responses to daily stress could subject at-risk individuals to higher atherosclerotic morbidity and mortality.

Working memory in schizophrenia and mania: Acute and subacute phases

Baekground: Patients with schizophrenia tend to have impaired performance on tests of working memory (WM). Neurocognitive models have linked WM to certain symptoms of schizophrenia. This study aimed to assess WM in schizophrenia and mania in the acute and subacute phases of the illness and explore correlations between WM and symptom clusters. Methods: A visuo-spatial delayed response task was used to assess WM in schizophrenia (n=20), mania (n= 14) and well controls (n=20). Patients were tested during the first week of an acute admission, and subjects were retested after four weeks. WM, symptoms (PANSS, TLC) and executive ability (COWAT, Stroop, Trail Making) were assessed at both time points. Results: When assessed for overall WM errors (both sensory and memory), there was a significant group difference (F- 11.53, df 2, 40; p

Psychophysiological phenotypes of cognition: The P3 and SW components

As part of a large ongoing project, the Memory, Attention and Problem Solving (MAPS) study, we investigated whether genetic variability explains some of the variance in psychophysiological correlates of brain function, namely, the P3 and SW components of event-related potentials (ERPs). These ERP measures are minute time recordings of brain processes and, because they reflect fundamental cognitive processing, provide a unique window on the millisecondto- millisecond transactions that occur at the cognitive level and taking place in the human brain. The extent to which the variance in P3 and SW components is influenced by genetic factors was examined in 350 identical and nonidentical twin pairs aged 16 years. ERPs were recorded from 15 scalp electrodes during the performance of a visuospatial delayed response task that engages working memory. Multivariate genetic analyses using MX were used to estimate genetic and environmental influences on individual differences in brain functioning and to identify putative genetic factors common to the ERP measures and psychometric IQ. For each of the ERP measures, correlation among electrode sites was high, a spatial pattern was evident, and a large part of the genetic variation in the ERPs appeared to be mediated by a common genetic factor. Moderate within-pair concordance in MZ pairs was found for all ERP measures, with higher correlations found for P3 than SW, and the MZ twin pair correlations were approximately twice the DZ correlations, suggesting a genetic influence. Correlations between ERP measures and psychometric IQ were found and, although moderately low, were evident across electrode site. The analyses show that the ERP components, P3 and SW, are promising phenotypes of the neuroelectrical activity of the brain and have the potential to be used in linkage and association analysis in the search for QTLs influencing cognitive function.

Genetic influence on ERP slow wave measures of working memory

Individual differences in the variance of event-related potential (ERP) slow wave (SW) measures were examined. SW was recorded at prefrontal and parietal sites during memory and sensory trials of a delayed-response task in 391 adolescent twin pairs. Familial resemblance was identified and there was a strong suggestion of genetic influence. A common genetic factor influencing memory and sensory SW was identified at the prefrontal site (accounting for an estimated 35%-37% of the reliable variance) and at the parietal site (51%-52% of the reliable variance). Remaining reliable variance was influenced by unique environmental factors. Measurement error accounted for 24% to 30% of the total variance of each variable. The results show genetic independence for recording site, but not trial type, and suggest that the genetic factors identified relate more directly to brain structures, as defined by the cognitive functions they support, than to the cognitive networks that link them.

Genetic covariance among measures of information processing speed, working memory, and IQ

The genetic relationship between lower (information processing speed), intermediate (working memory), and higher levels (complex cognitive processes as indexed by IQ) of mental ability was studied in a classical twin design comprising 166 monozygotic and 190 dizygotic twin pairs. Processing speed was measured by a choice reaction time (RT) task (2-, 4-, and 8-choice), working memory by a visual-spatial delayed response task, and IQ by the Multidimensional Aptitude Battery. Multivariate analysis, adjusted for test-retest reliability, showed the presence of a genetic factor influencing all variables and a genetic factor influencing 4- and 8-choice RTs, working memory, and IQ. There were also genetic factors specific to 8-choice RT, working memory, and IQ. The results confirmed a strong relationship between choice RT and IQ (phenotypic correlations: -0.31 to -0.53 in females, -0.32 to -0.56 in males; genotypic correlations: -0.45 to -0.70) and a weaker but significant association between working memory and IQ (phenotypic: 0.26 in females, 0.13 in males; genotypic: 0.34). A significant part of the genetic variance (43%) in IQ was not related to either choice RT or delayed response performance, and may represent higher order cognitive processes.

Event-related potential correlates of impaired visuospatial working memory in schizophrenia

Previous studies have reported that patients with schizophrenia demonstrate impaired performance during working memory (WM) tasks. The current study aimed to determine whether WM impairments in schizophrenia are accompanied by reduced slow wave (SW) activity during on-line maintenance of mnemonic information. Event-related potentials were obtained from patients with schizophrenia and well controls as they performed a visuospatial delayed response task. On 50% of trials, a distractor stimulus was introduced during the delay. Compared with controls, patients with schizophrenia produced less SW memory negativity, particularly over the right hemisphere, together with reduced frontal enhancement of SW memory negativity in response to distraction. The results indicate that patients with schizophrenia generate less maintenance phase neuronal activity during WM performance, especially under conditions of distraction.

Altered plasma response to zinc and iron tolerance test after Roux-en-Y gastric bypass

Background: The duodenum and proximal jejunum are excluded after Roux-en-Y gastric bypass but these intestinal sites are where iron and zinc are most absorbed. Therefore, they are among the nutrients whose digestive and absorptive process can be impaired after surgery. The aim of the present study was to investigate the iron and zinc plasma response to a tolerance test before and after bariatric surgery. The study was performed at Sao Paulo University School of Medicine of Ribeirao Preto, Brazil. Methods: In a longitudinal paired study, 9 morbidly obese women (body mass index >= 40 kg/m(2)) underwent an iron and zinc tolerance test before and 3 months after surgery. The iron and zinc levels were determined at 0, 1, 2, 3, and 4 hours after a physiologic unique oral dose. The mineral concentrations in die plasma and 24-hour urine sample were assayed using an atomic absorption spectrophotometer. The anthropometric measurements and 3-day food record were also evaluated. A linear mixed model was used to compare the plasma concentration versus interval after the oral dose, before and after surgery. Results: The pre- and postoperative test results revealed a significantly lower plasma zinc response (P <.01) and a delayed response to iron intake after surgery. The total plasma iron concentration area, during the 4 hours, was not different after surgery (P >.05). The 24-hour urinary iron and zinc excretion did not differ between the pre- and postoperative phases. Conclusion: The present data showed a compromised response to the zinc tolerance test after gastric bypass surgery, suggesting an impaired absorption of zinc. More attention must be devoted to zinc nutritional status after surgery. (Surg Obes Relat Dis 2011;7:309-314.) (C) 2011 American Society for Metabolic and Bariatric Surgery. All rights reserved.