Henry A. Buchtel

Frontal lobe lesions in man cause difficulties in suppressing reflexive glances and in generating goal-directed saccades

SummaryThe frontal eye field (FEF) and superior colliculus (SC) are thought to form two parallel systems for generating saccadic eye movements. The SC is thought classically to mediate reflex-like orienting movements. Thus it can be hypothesized that the FEF exerts a higher level control on a visual grasp reflex. To test this hypothesis we have studied the saccades of patients who have had discrete unilateral removals of frontal lobe tissue for the relief of intractable epilepsy. The responses of these patients were compared to those of normal subjects and patients with unilateral temporal lobe removals. Two tasks were used. In the first task the subject was instructed to look in the direction of a visual cue that appeared unexpectedly 12° to the left or right of a central fixation point (FP), in order to identify a patterned target that appeared 200 ms or more later. In the second “anti-saccade” task the subject was required to look not at the location of the cue but in the opposite direction, an equal distance from FP where after 200 ms or more the patterned target appeared. Three major observations have emerged from the present study. (a) Most frontal patients, with lesions involving both the dorsolateral and mesial cortex had long term difficulties in suppressing disallowed glances to visual stimuli that suddenly appeared in peripheral vision. (b) In such patients, saccades that were eventually directed away from the cue and towards the target were nearly always triggered by the appearance of the target itself irrespective of whether or not the “anti-saccade” was preceded by a disallowed glance. Those eye movements away from the cue were only rarely generated spontaneously across the blank screen during the cue-target time interval. (c) The latency of these visually-triggered saccades was very short (80–140 ms) compared to that of the correct saccades (170–200 ms) to the cue when the cue and target were on the same side, thereby suggesting that the structures removed in these patients normally trigger saccades after considerable computations have already been performed. The results support the view that the frontal lobes, particularly the dorsolateral region which contains the FEF and possibly the supplementary motor area contribute to the generation of complex saccadic eye-movement behaviour. More specifically, they appear to aid in suppressing unwanted reflex-like oculomotor activity and in triggering the appropriate volitional movements when the goal for the movement is known but not yet visible.

Spatial compatibility and anatomical factors in simple and choice reaction time.

Abstract Simple reaction time to a lateralized unstructured visual stimulus was studied in subjects with hands crossed or uncrossed. Regardless of the hand position, the right hand was faster than the left hand when the stimulus was to the right of fixation, and vice versa. In both conditions there was a left visual field superiority. In a second experiment the same lateralized stimuli were presented to subjects with hands crossed or uncrossed who had to decide which hand to use depending on the position of the stimulus. In this experiment the faster hand was the one in the same visual space as the stimulus (spatial compatibility). We conclude that in simple reaction time experiments the difference between ipsilateral and contralateral reactions is due to the elementary anatomical connectivity, and that spatial compatibility becomes important only in choice situations.

Hemispheric superiority in reaction time to faces: a sex difference.

In males but not females, reaction time to faces is faster when stimuli are presented to the right hemisphere than when presented to the left hemisphere. The complete lack of a hemispheric difference in females suggests that with brief exposure and immediate judgement, a lateralized mechanism specialized for faces can be activated only in males.

Spatial attentional shifts: Implications for the role of polysensory mechanisms

Simple reaction times to lateralized visual (Experiment 1) or auditory (Experiment 2) targets were studied in normal subjects. The targets were preceded by a visual or auditory cue located on the same (valid cue), or opposite (invalid cue) side as the subsequent target, or on both sides (neutral cue), with one of four cue target intervals. The validity of visual and auditory cues influenced the speed of response to the visual target but not to the auditory target. It is hypothesized that cross-modal cueing of spatial position works only with modalities for which a movement (e.g. saccade) leads to improved sensory analysis.

Verbal Fluency and Positron Emission Tomographic Mapping of Regional Cerebral Glucose Metabolism

Impairment in verbal fluency (VF) has been a consistently reported clinical feature of focal cerebral deficits in frontal and temporal regions. More recent behavioral activation studies with healthy control subjects using positron emission tomography (PET), however, have noted a negative correlation between performance on verbal fluency tasks and regional cortical activity. To see if this negative relationship extends to steady-state non-activation PET measures, thirty-three healthy adults were given a VF task within a day of their 18F-2-fluoro-2-deoxy-D-glucose PET scan. VF was found to correlate positively with left temporal cortical region metabolic activity but to correlate negatively with right and left frontal activity. VF was not correlated significantly with right temporal cortical metabolic activity. Some previous studies with normals using behavioral activation paradigms and PET have reported negative correlations between metabolic activity and cognitive performance similar to that reported here. An explanation for the disparate relationships that were observed between frontal and temporal brain areas and VF might be found in the mediation of different task demands by these separate locations, i.e., task planning and/or initiation by frontal regions and verbal memory by the left temporal area.

Neuronal plasticity: historical roots and evolution of meaning

In this paper, we outline some important milestones in the history of the term “plasticity” in reference to the nervous system. Credit is given to William James for first adopting the term to denote changes in nervous paths associated with the establishment of habits; to Eugenio Tanzi for first identifying the articulations between neurons, not yet called synapses, as possible sites of neural plasticity; to Ernesto Lugaro for first linking neural plasticity with synaptic plasticity; and to Cajal for complementing Tanzi’s hypothesis with his own hypothesis of plasticity as the result of the formation of new connections between cortical neurons. Cajal’s early use of the word plasticity is demonstrated, and his subsequent avoidance of the term is tentatively accounted for by the fact that other authors extended it to mean neuronal reactions partly pathological and no doubt quite different from those putatively associated with normal learning. Evidence is furnished that in the first two decades of the twentieth century the theory was generally accepted that learning is based on a reduced resistance at exercized synapses, and that neural processes become associated by coactivation. Subsequently the theory fell in disgrace when Lashley’s ideas about mass action and functional equipotentiality of the cortex tended to outmode models of the brain based on orthodox neural circuitry. The synaptic plasticity theory of learning was rehabilitated in the late 1940s when Konorski and particularly Hebb argued successfully that there was no better alternative way to think about the modifiability of the brain by experience and practice. Hebb’s influential hypothesis about the mechanism of adult learning contained elements strikingly similar to the early speculations of James, Tanzi and Cajal, but Hebb did not acknowledge specifically these roots of his thinking about the brain, though he was fully aware that he had resurrected old ideas wrongly neglected for a long time. Lately the concept of neural plasticity has been complicated by attributing considerably different meanings to it. A scholarly paper by Paillard is used to show how an analysis in depth can clarify some confusion engendered by an unrestricted use of the concept and term of neural plasticity.

Spatial attentional shifts: Further evidence for the role of polysensory mechanisms using visual and tactile stimuli

Normal subjects performed simple reaction time responses to lateralized visual target stimuli (Experiment 1) and lateralized tactile target stimuli (Experiment 2). In each experiment, the lateralized targets were preceded at one of four intervals by a visual or tactile cue located on the same (valid cue), or opposite (invalid cue) side, or on both sides (neutral cue). The validity of the visual and tactile cues influenced the speed of response to either target stimulus. These findings, together with those previously reported (Buchtel and Butter, Neuropsychologia 26, 499-509, 1988), are consistent with the view that intra- and inter-modal spatial cueing is effective with modalities that are linked to orienting systems in which movements of the sensory array serve to improve sensory analysis.

Serial Cognitive Testing in Temporal Lobe Epilepsy: Longitudinal Changes with Medical and Surgical Therapies

Summary: Cognitive testing was repeated at intervals ranging from 1 to 8 years in 47 adult patients with temporal lobe epilepsy (TLE). Each patient underwent standardized batteries, including the Wechsler Adult Intelligence Scale, Revised (WAIS‐R), and Wechsler Memory Scale (WMS). Both surgically treated and nonsurgical patients were examined. The nonsurgical group underwent serial testing for clinical indications, usually for complaints of memory dysfunction. Longitudinal testing could not verify any mean deterioration of intellect or memory in this group; variance over time was similar to test‐retest norms in healthy controls. WAIS‐R scores before and after resection in the surgical group were similar to our serial WAIS‐R data in nonsurgical patients. When we divided surgical patients according to side of epileptogenesis, we noted the expected differences in verbal and visual memory. Right‐sided surgery patients improved significantly in Full‐scale IQ (FSIQ) and tended to improve in logical memory on postoperative testing. Patients undergoing left resections had no retest improvement and tended to show decrease in several measures of verbal memory. Our findings should stimulate continued investigation into the natural history of lateralized memory and intellectual function in epilepsy, particularly to clarify longterm cognitive outcome in nonsurgical patients.

Presurgery Expectations, Postsurgery Satisfaction, and Psychosocial Adjustment After Epilepsy Surgery

Summary: Purpose: The medical benefits of epilepsy surgery are well documented, but the psychosocial consequences of surgery have received less attention. This is especially true of the roles of expectations and satisfaction in postsurgery functioning. The present study was designed to examine the relationships between expectation, satisfaction with surgery, and psychosocial functioning in patients and their significant others before and after epilepsy surgery.

Analysis of the Activity Evoked in the Cerebellar Cortex by Stimulation of the Visual Pathways

SummaryIn cats without general anaesthesia electric stimulation of the optic chiasma evoked usually in the depth of the cerebellar cortex of lobuli VI and VII a sequence of waves at a latency of 7–10 msec which have been shown to be due to the mossy fibre input. A later wave at a latency of 18–20 msec was also sometimes found in isolation or in association with the early wave. This later field has been identified as due to the climbing fibre input. Unitary recordings have given support to this interpretation. Some correlation has been made with recordings obtained by electric stimulation of the superior colliculus and by flash stimulation of the retinae.It is concluded that the optic pathways project to the visual area of the cerebellar cortex through both mossy and climbing fibre inputs, although from this study based mainly on the laminar analysis of evoked fields, the former input seems to be more widespread and more consistently obtained than the latter.