Processes contributing to forward and backward span: an ERP investigation

Differences in Verbal and Visuospatial Forward and Backward Order Recall: A Review of the Literature

How sequential, verbal and visuospatial stimuli are encoded and stored in memory is not clear in cognitive psychology. Studies with order recall tasks, such as the digit, and Corsi span, indicate that order of presentation is a crucial element for verbal memory, but not for visuospatial memory. This seems to be due to the different effects of forward and backward recall in verbal and visuospatial tasks. In verbal span tasks, performance is worse when recalling things in backward sequence rather than the original forward sequence. In contrast, when it comes to visuospatial tasks, performance is not always worse for a modified backward sequence. However, worse performance in backward visuospatial recall is evident in individuals with weak visuospatial abilities; such individuals perform worse in the backward version of visuospatial tasks than in the forward version. The main aim of the present review is to summarize findings on order recall in verbal and visuospatial materials by considering both cognitive and neural correlates. The results of this review will be considered in the light of the current models of WM, and will be used to make recommendations for future studies.

The relationship between Hippocampal asymmetry and working memory processing in combat-related PTSD - a monozygotic twin study

BACKGROUND

PTSD is associated with reduction in hippocampal volume and abnormalities in hippocampal function. Hippocampal asymmetry has received less attention, but potentially could indicate lateralised differences in vulnerability to trauma. The P300 event-related potential component reflects the immediate processing of significant environmental stimuli and has generators in several brain regions including the hippocampus. P300 amplitude is generally reduced in people with PTSD.

METHODS

Our study examined hippocampal volume asymmetry and the relationship between hippocampal asymmetry and P300 amplitude in male monozygotic twins discordant for Vietnam combat exposure. Lateralised hippocampal volume and P300 data were obtained from 70 male participants, of whom 12 had PTSD. We were able to compare (1) combat veterans with current PTSD; (2) their non-combat-exposed co-twins; (3) combat veterans without current PTSD and (4) their non-combat-exposed co-twins.

RESULTS

There were no significant differences between groups in hippocampal asymmetry. There were no group differences in performance of an auditory oddball target detection task or in P300 amplitude. There was a significant positive correlation between P300 amplitude and the magnitude of hippocampal asymmetry in participants with PTSD.

CONCLUSIONS

These findings suggest that greater hippocampal asymmetry in PTSD is associated with a need to allocate more attentional resources when processing significant environmental stimuli.

Age effects on the P300 potential and the corresponding fMRI BOLD-signal

Age has been reported to influence amplitude and latency of the P300 potential. Nevertheless, it is not yet fully understood which brain regions are responsible for these effects. The aim of this study was to investigate age-effects on the P300 potential and the simultaneously acquired BOLD signal of functional MRI. 32 healthy male subjects were investigated using an auditory oddball paradigm. The functional MRI data were acquired in temporal synchrony to the task. The evoked potential data were recorded during the intervals in between MR image acquisitions in order to reduce the influence of the scanner noise on the presentation of the tones and to reduce gradient artifacts. The age-effects were calculated by means of regression analyses. In addition, brain regions modulated by the task-induced amplitude variation of the P300 were identified (single trial analysis). The results indicated an age effect on the P300 amplitude. Younger subjects demonstrated increased parietal P300 amplitudes and increased BOLD responses in a network of brain regions including the anterior and posterior cingulate cortex, the insula, the temporo-parietal junction, the superior temporal gyrus, the caudate body, the amygdala and the parahippocampal gyrus. Single trial coupling of EEG and fMRI indicated that P300 amplitudes were predominantly associated with neural responses in the anterior cingulate cortex, the putamen and temporal brain areas. Taken together, the results indicate diminished neural responses in older compared to younger subjects especially in frontal, temporo-parietal and subcortical brain regions.

Electrophysiological indices of altered working memory processes in long-term ecstasy users

OBJECTIVE

The aim of this study was to determine the effect of light long-term ecstasy consumption on verbal short-term and working memory and to identify the cognitive processes contributing to task performance.

METHOD

Electroencephalogram was recorded while ecstasy users (N = 11), polydrug users (N = 13), and non-users (N = 13) completed forward and backward serial recognition tasks designed to engage verbal short-term memory and verbal working memory, respectively.

RESULTS

All three groups displayed significantly lower digit-backward span than digit-forward span with ecstasy users displaying the greatest difference. The parietally distributed P3b was significantly smaller in the digits backward task than in the digits forward task in non-ecstasy-using controls. Ecstasy users did not show the reduced P3b component in the backward task that was seen in both non-ecstasy-using control groups.

CONCLUSIONS

Ecstasy users' performance was suppressed more by the concurrent processing demands of the working memory task than that of the non-ecstasy-using controls. Non-ecstasy-using controls showed differential event-related potential wave forms in the short-term and working memory tasks, and this pattern was not seen in the ecstasy users. This is consistent with a reduction in the cognitive resources allocated to processing in working memory in ecstasy users.

Cognitive correlates of mathematical achievement in children with cerebral palsy and typically developing children

BACKGROUND

Remarkably few studies have investigated the nature and origin of learning difficulties in children with cerebral palsy (CP).

AIMS

To investigate math achievement in terms of word-problem solving ability in children with CP and controls. Because of the potential importance of reading for word-problem solving, we investigated reading as well.

SAMPLE

Children with CP attending either special (n= 41) or mainstream schools (n= 16) and a control group of typically developing children in mainstream schools (n= 16).

METHOD

Group differences in third grade math and reading, controlled for IQ, were tested with analyses of co-variance (ANCOVAs). Hierarchical regression was used to investigate cognitive correlates of third grade math and reading. Predictors included verbal and non-verbal IQ measured in first grade, components of working memory (WM) and executive function (EF) measured in second grade, and arithmetic fact fluency and reading measured in third grade.

RESULTS

Children with CP in special schools performed significantly worse than their peers on word-problem solving and reading. There was a trend towards worse performance in children with CP in mainstream schools compared to typically developing children.

CONCLUSIONS

Impairments of non-verbal IQ and WM updating predicted future difficulties in both word-problem solving and reading. Impairments of visuospatial sketchpad and inhibition predicted future word-problem, but not reading difficulty. Conversely, deficits of phonological loop predicted reading but not word-problem difficulty. Concurrent arithmetic fact fluency and reading ability were both important for word-problem solving ability. These results could potentially help to predict which children are likely to develop specific learning difficulties, facilitating early intervention.