Biomedical subjects

Richard A P Roche

Publications and source records attributed to Richard A P Roche.

5 recordsLinked to original sources

PubMed2006

Electrophysiological and information processing variability predicts memory decrements associated with normal age-related cognitive decline and Alzheimer's disease (AD).

Recent theoretical models of cognitive aging have implicated increased intra-individual variability as a critical marker of decline. The current study examined electrophysiological and information processing variability and memory performance in normal younger and older controls, and older adults with Alzheimer's disease (AD). It was hypothesized that higher levels of variability would be indicative of age-related and disease-related memory deficits. Results indicated both implicit and explicit memory deficits associated with AD. Consistent with previous research, behavioral speed and variability emerged as sensitive to age- and disease-related change. Amplitude variability of P3 event-related potentials was a unique component of electrophysiological activity and accounted for significant variance in reaction time (RT) mean and RT standard deviation, which in turn accounted for significant variance in memory function. Results are discussed in light of theoretical and applied issues in the field of cognitive aging.

Adult↗

PubMed2005

Individual differences discriminate event-related potentials but not performance during response inhibition.

Event-related brain potentials (ERPs) were recorded from 20 normal participants while they completed a Go/NoGo response inhibition task. Previous ERP studies have implicated the N2 and P3 waveforms as the main indices of processing in this task, and functional brain imaging has shown parietal, prefrontal and anterior cingulate cortices to be involved in response inhibition. 32-channel ERP analysis revealed amplitude differences in the N2/P3 components when stimuli that required a button-press (Go stimuli) were compared with stimuli for which the response had to be withheld (No-Go stimuli), and in N2 and P3 latencies when successful withholds to No-Go stimuli were compared with unsuccessful attempts to inhibit. Further differences in the N2/P3 complex emerged when participants were grouped in terms of a measure of absentmindedness (the Cognitive Failures Questionnaire, CFQ); larger and earlier components were found for high CFQ respondents. We conclude that the latencies of the N2 and P3 may be the critical indicators of active inhibitory processes for this task, suggesting that a pattern of sequential activation rather than altered activity level in key structures may mediate success on the task. In addition, highly absentminded participants exhibited larger components for errors than did less absentminded participants when performing at the same level, which implies that the absentminded may require greater activity in the neural substrates of response inhibition in order to accomplish this task at a comparable level of performance to less absentminded participants.

Adolescent↗

PubMed2004

EEG alpha power changes reflect response inhibition deficits after traumatic brain injury (TBI) in humans.

Brain damage due to traumatic brain injury (TBI) has been associated with deficits in executive functions and the dynamic control of behaviour. Event-related brain potentials and spectral power data were recorded from eight TBI participants and eight matched controls while they completed a Go/NoGo response inhibition task. The TBI group was found to be significantly impaired at the task compared to controls, and exhibited abnormal N2 and P3 waveform components in response to NoGo stimuli relative to controls. Significant correlations were also found between alpha power, Go-trial RT and errors. We conclude that abnormal activity in the structures damaged in this group may render such patients less capable of maintaining a state of alpha desynchronisation compared to controls, resulting in poorer performance on the task.

Adult↗

PubMed2004

Behavioural and physiological impairments of sustained attention after traumatic brain injury.

Sustaining attention under conditions of low external demand taxes our ability to stay on task and to avoid more appealing trains of thought or environmental distractions. By contrast, a stimulating, novel environment engages attention far more freely without the subjective feeling of having to override monotony. Our ability to maintain a goal-directed focus without support from the environment requires the endogenous control of behaviour. This control can be modulated by fronto-parietal circuits and this ability is compromised following traumatic brain injury (TBI) leading to increased lapses of attention. In this paper, we further explore a laboratory paradigm that we argue is particularly sensitive to sustained attention as opposed to other aspects of attentional control involving the selection and management of goals in working memory. The paradigm (fixed sequence Sustained Attention to Response Task--SARTfixed) involves withholding a key press to an infrequent no-go target embedded within a predictable sequence of numbers. We demonstrate that TBI patients in this study make disproportionately more errors than controls on this task. An analysis of response times (RTs) and EEG alpha power across the task demonstrates group differences preceding the critical no-go trial. Controls demonstrate a lengthening of RTs accompanied by desynchronization of power within the alpha band (approximately 10 Hz) preceding the no-go trial. Conversely, the TBI group showed a shortening of RTs during this period with no evidence of alpha desynchronization. These findings suggest that TBI patients may have dysfunctional alpha generators as a consequence of their injury that impairs endogenous control during the task.

Adult↗

PubMed2003

Behavioural and electrophysiological correlates of visuomotor learning during a visual search task.

Visuomotor association learning involves learning specific motor responses to arbitrary cues, and is dependent on a distributed and highly flexible network in the brain. We investigated the behavioural and electrophysiological correlates of arbitrary visuomotor learning in 20 normal participants. An experimental group learned an arbitrary association between a visual stimulus and a motor response during a training block. Their performance was compared with that of untrained controls on a subsequent visual discrimination task in which the learned association was a crucial element. Event-related brain potentials (ERPs) were recorded from the scalp of each participant during learning and discrimination blocks. Reaction times to stimuli in the discrimination task were significantly faster in the trained group compared to controls. There was a corresponding difference in the ERP waveforms recorded during the task, with larger P3b amplitude for the trained group over midline and centroparietal scalp areas. A latency difference in P3b was also observed for trained targets compared to distractors. RTs during the training block decreased in a manner consistent with learning effects. We conclude that training of a visuomotor association facilitates subsequent performance on a related task, and that the waveform correlates found here may reflect the involvement of parts of the network underlying arbitrary association mapping.

Adult↗