Stuart R. Butler

Amnesia after transection of the fornix in monkeys: Long-term memory impaired, short-term memory intact

Monkeys in whom the fornix had been transected and controls were trained on two versions of delayed non-matching to sample (DNMS). On DNMS-LSS the stimulus pair for each trial was selected from a large set of junk objects so that the animals saw particular stimuli infrequently. On DNMS-RS the same two stimuli were presented repeatedly. Memory for the sample was assessed with retention intervals of 10, 70 and 130 sec spent either in the dark or with levels of illumination designed to promote interference effects. On DNMS-LSS the lesioned animals were impaired, being more susceptible than controls to increases in the retention interval. However, neither group was particularly sensitive to interference. In contrast, on DNMS-RS the lesioned monkeys were unimpaired, both groups showing a marked decrement in performance with increasing retention interval and a high sensitivity to the effects of interference. These data suggest that monkeys possess a short-term memory which is intact after transection of the fornix and a long-term memory which is not.

Cognitive style and individual differences in EEG alpha during information processing

Abstract When presented with a task, it was hypothesised that different people tend to process the same information in different ways, using different areas of the brain, depending upon their cognitive style. The study used 15 adult subjects, who received the computer‐presented Cognitive Styles Analysis to assess their positions on two basic cognitive style dimensions: the Wholist‐Analytic and Verbal‐Imagery. In a computer‐presented task, subjects were asked to view words presented singly at a rate of two, five and 10 words/second and in pairs at five and 10 word‐pairs/second and to press a key when a word appeared which was in a target conceptual category (e.g. a fruit). The task comprised eight 30‐second trials. During the task, alpha band EEG was monitored at 15 locations. For the Wholist‐Analytic style, Analytics had, over all tasks, lower alpha power relative to the Wholists at all locations, and particularly posteriorly. With the Verbal‐Imagery dimension, there was style‐hemisphere effect, with Verb...

Sex Differences in Human Cerebral Function

Publisher Summary Psychometric studies have revealed a number of statistically significant differences between male and female populations with respect to cognitive ability and hand preference. This chapter describes sex differences in the functions of human cerebrum. It is hard to see why greater differentiation of hemispheric function in the men should lead the sexes to excel in skills that depend upon opposite sides of the brain. Electroencephalography EEG studies of lateralization are divided on the question of simple sex differences. There are reports that the male brain is functionally more asymmetric than the female, and there are negative findings. The balance of opinion seems to favor the former position, especially because there are no valid reports of greater asymmetry in females. Although a tendency toward right––rather than left––hemisphere, EEG activation appears to be conferred by both familial left-handedness and by being male, it is as yet still obscure whether these two factors affect the lability of cognitive strategy, the degree of lateralisation, and other aspects of the organization of cerebral function in a similar fashion.

Hemispheric asymmetry of EEG alpha activation: Effects of gender and familial handedness

Twenty-four male and twenty-four female undergraduates took part in an experiment to investigate the effects of gender and familial handedness on hemispheric activation during numeric and visuospatial thinking. Each gender group was divided into twelve subjects with close left handed relatives and twelve subjects without. All subjects were overtly right handed. EEG alpha activity was recorded from left and right occipital and parietal regions with respect to mastoid references while the subjects performed numeric tasks with eyes open and with eyes closed, a face-recognition and a tactile-discrimination (figural-unification) task. EEG alpha power was quantified during these conditions and during relaxed wakefulness with eyes open and eyes closed. Relative activation, (suppression of alpha activity from rest) of left and right parietal regions during numeric and spatial tasks was found to depend upon gender and familial handedness. Males, not females, tended to switch from left hemisphere activation during face recognition. Irrespective of gender and to some extent of task, a tendency towards greater activation of the right hemisphere was associated with the possession of left handers among close relatives.

Asymmetries in the CNV over left and right hemispheres while subjects await numeric information

Abstract The contingent negative variation (CNV) was recorded from frontal and central electrodes in one left-handed and 12 right-handed subjects. The CNV was elicited by tachistoscopically exposed visual stimuli comprising a warning spot followed by a numeral. Numerals so exposed had to be memorized (cumulative condition), added (arithmetic condition), or checked to ensure that all were zeros (repetitive condition). The arithmetic and cumulative tasks were designed to potentiate any expectancy mechanisms in the hemisphere dominant for verbal processes. The repetitive task was intended as a neutral control. All three tasks elicited CNVs whose amplitude was greater over the hemisphere contralateral to the preferred hand. The results are discussed in terms of possible relationships with handedness and the lateralization of cerebral function.

The effects of visual cortex lesions on the perception of rotated shapes

Monkeys with inferior temporal cortex lesions cannot discriminate between different shapes (e.g., + vs. O) but can discriminate between shapes that differ only in orientation (e.g., 6 vs 9). Lesions of the parietal cortex, on the other hand, impair the discrimination of rotated shapes but spare the ability to discriminate between different shapes. A similar dissociation is found between some visual agnosics who can match but not identify rotated views of objects and other patients who can identify and discriminate objects only if the view is conventional; any change in orientation disrupts performance. In this paper we argue that two mechanisms may be available for the perception of rotated shapes. Which mechanism is used depends on the degree of rotation. It is suggested that the different effects of parietal and temporal lesions reflect the relative contributions of the two areas to the task and disrupt different stages of the two strategies used. A framework for the cortical processing of rotated shapes in the non-human primate is presented.

Does amnesia after transection of the fornix in monkeys reflect abnormal sensitivity to proactive interference

Monkeys in whom the fornix had been transected and controls were tested in two versions of delayed non-matching to sample (DNMS). On DNMS-LSS both of the stimuli for each trial were selected from a large set of junk objects that were already familiar to the subjects. On DNMS-CSN the new stimulus at the retention test of each trial was one which the animals had never encountered before. Memory for the sample was assessed with retention intervals of 10, 70 and 130 s. In DNMS-LSS the lesioned animals were impaired, being more susceptible than controls to increases in the retention interval. However, no impairment in DNMS-CSN was observed. The abnormally fast forgetting by lesioned animals in DNMS-LSS seems therefore to reflect abnormal sensitivity to proactive interference. The results are compared with similar findings from amnesic humans and their implications for theoretical accounts of the effects of hippocampal disruption are discussed.

Asymmetries of the contingent negative variation (CNV) and its after positive wave (APW) related to differential hemispheric involvement in verbal and non-verbal task

The CNV and the subsequent positive wave (including both the P300 wave and the slow positivity following it) were recorded at left and right frontal and central electrodes during the performance of tasks in which nine right-handed subjects (male and female) had to determine whether S1 and S2 were the same or different. In one task, works had to be matched for meaning while in a second, faces had to be matched for identity. Words elicited CNVs which were more negative over left than right frontal regions. This effect was reversed when the stimuli were faces. Since the CNV is presumed to reflect processes of anticipation rather than stimulus processing, the asymmetry cannot be explained in terms of the lateralisation of neural mechanisms specialised for the analysis of verbal or visuospatial stimuli. Instead the observation is regarded as evidence for mechanisms of lateral activation of a more general nature than would be necessary for the facultative selection of cognitive mode. The amplitude of the CNV relative to baseline was affected by the amplitude of P300 response to S1. This was larger to faces than words in both hemispheres. A small asymmetry in the positive wave following S2 was observed, the amplitude being greater over the right hemisphere for words and over the left for faces. This is interpreted in terms of the subjective probability of the two types of stimulus for a hemisphere ill-equipped to receive them.

The effects of fornix lesions on latent learning in the rat

Abstract Rats with fornix lesions and sham-operated controls were trained to press a lever for 0.9% NaCl while thirsty and then tested under extinction conditions when not thirsty. Sham-operated controls which were sodium depleted during extinction testing made twice as many responses as non-depleted controls, an effect attributed to latent learning. However, no such difference was observed between the sodium depleted and the non-depleted subjects which had received fornix lesions, suggesting that fornix lesions abolish this type of latent learning. This effect is predicted by both cognitive map and contextual retrieval models of hippocampal function.

Individual Differences in the Asymmetry of Alpha Activation

Asymmetry in the distribution of the alpha rhythm first received attention during the early seventies (Morgan, McDonald and MacDonald, 1971; Galin and Ornstein, 1972a & b; Glass and Butler, 1973; Butler and Glass, 1974). The effect was attributed to the activation of lateralised mechanisms serving language and ‘visuospatial’ functions and was therefore perceived as a non-invasive method of investigating hemispheric specialisation. It has recently become clear that alpha asymmetry varies systematically as a function of gender and handedness. In this chapter we shall consider the significance of this variation in terms of individual differences in the structural and dynamic aspects of hemispheric specialisation.