Lateralized brain damage, sex differences, and the Wechsler Intelligence Scales: a reexamination of the literature

Gender differences in post-temporal lobectomy verbal memory and relationships between MRI hippocampal volumes and preoperative verbal memory

Thirty-three men and 42 women who underwent left, and 26 men and 24 women who underwent right temporal lobectomy (TL) were studied retrospectively to determine if there were sex differences in (1) verbal memory outcome, and (2) relationships between verbal memory and magnetic resonance imaging (MRI) hippocampal volumes. All patients were left hemisphere language dominant. The surgical specimen and MRI were consistent only with mesial temporal sclerosis (MTS). Verbal memory was evaluated by Logical Memory percent retention (LMPER) from the Wechsler Memory Scale-Revised (WMS-R). Women experienced a significant improvement while men experienced a significant decline in postoperative LMPER. The difference between right and left hippocampal volumes predicted verbal memory outcome in both men and women. Preoperative LMPER was positively correlated with both the left and right hippocampal volumes in left TL women only. No verbal memory sex differences or correlations between LMPER and MRI data were found in the right TL group. The data support the presence of human neurocognitive sexual dimorphism. Verbal memory abilities supported by the hippocampus are less lateralized in women with left temporal lobe epilepsy and mesial temporal sclerosis. Women appear to have greater verbal memory plasticity following early left mesial temporal lobe insult.

MRI hippocampal volume and neuropsychology in epilepsy surgery

A review is provided of recent findings on relationships between neurocognitive test data and magnetic resonance imaging (MRI)-determined hippocampal volumes in nonlesional temporal lobectomy patients. The difference between the right and left hippocampal volumes is correlated with postoperative verbal memory in left temporal lobectomy patients who do not have lesional pathology. MRI hippocampal volume data are not associated with measures of executive functioning or naming. Sex differences have been found for verbal memory outcome as women have better verbal memory following left temporal lobectomy. Sex differences have also been found in the relationships between verbal and visual memory, and hippocampal volume data. The systematic combination of MRI-acquired morphological data and neuropsychological test data may further our understanding of neurocognitive function, and provide clinically useful data for counseling epilepsy surgery patients. The current data are promising with regard to prediction of memory outcome following temporal lobectomy, but they do not yet allow for prediction of specific individual patient outcomes. Rather, the currently available data support counseling patients based on the memory outcome of others with similar characteristics.

Forgetting rates for verbal, pictorial, and figural stimuli

Literature on forgetting rates is reviewed and related methodological issues are discussed. Descriptive data from 50 subjects are provided for tests which were developed to assess forgetting rates for words, pictures and designs. The three tests are well-matched on initial learning at criterion and have comparable variance and skewness of score distributions. Forgetting rates were similar across the initial 10-min retention interval, but there was a more rapid loss of words than pictures and designs from 10 min to 2 hr, especially in male subjects. Memory for words and pictures steadily declined between 10 min and 48 hr, but there was no further loss for designs after 2 hr. These findings suggest that nonverbal memory storage is more stable than verbal memory storage over intervals of hours to days. Modest sex differences are discussed in terms of potential differences in organization of brain function. The potential utility of these tests in further elucidating the nature of memory impairment in clinical populations is addressed.

Event-related potential evidence of sex differences in verbal and nonverbal memory tasks

ERPs were recorded from 19 scalp electrodes while 48 subjects (24 females) performed visual recognition tasks for recurring verbal items and recurring abstract figures. Reaction times were longer in the figures than verbal task; the latencies of the ERP components (P2, N4, P3, P4) were also longer for the figures. A nonreversing asymmetry (R greater than L) was seen in both tasks. Significant task by electrode interactions (for P3, P4) were found, due to larger amplitudes anteriorly for the figures, but larger amplitudes posteriorly for the verbal task. All ERP latencies were longer for males than females. There were sex by task by electrode interactions in the amplitudes, due to larger ERPs (P2, N4) for females anteriorly for the figures, but slightly larger posteriorly for the verbal task. These results suggest that sex differences in cognitive abilities may be based on differences in biological mechanisms.

Effects of arousal and directed attention on hemispheric asymmetry in a finger-tapping dual-task paradigm

In the present study we investigated the effects of concurrent verbal (reading) and nonverbal (humming) cognitive tasks on right- and left-hand finger-tapping in relation to hemispheric asymmetry in right- and left-handed females and males. The aim of the study was to investigate effects of attending either to the cognitive or manual task, and effects of differences in arousal attributed to the various tasks. The results revealed decreased finger-tapping frequency in males, and especially in right-handers, during execution of both the reading and humming task. For the reading task, the interference was lateralized, with a greater decrease in tapping frequency in the right hand. No interference was observed in the female groups. Biased attention to the cognitive or manual task did not have any effect on finger-tapping. However, increased arousal was observed during execution of the humming task, thus indicating this to be a mediating factor in finger-tapping interference.