Active Hemisphere Research Articles

A fateful encounter: Sixty years later—Reflections on the Wada test

A fateful encounter: Sixty years later—Reflections on the Wada test

Affective self-report during the intracarotid sodium amobarbital test: Group differences

Emotional reactions are sometimes observed during the intracarotid sodium amobarbital test. For instance, euphoric/indifference reactions can be seen during right hemisphere inactivation and catastrophic reactions may accompany left hemisphere inactivation. Less dramatic changes can also be detected in affective self-report during left and right hemisphere amobarbital tests, with more negative affect reported during left hemisphere inactivation and either neutral or mildly positive affective states reported during right hemisphere inactivation. The current study not only replicated this effect, but in addition, found significant group differences. The first group (right way) showed a pattern of affective self-report during left and right amobarbital tests entirely consistent with prior findings, while a second group (wrong way) showed results that behaved in a diametrically opposite fashion. A third group (no change) showed little, if any, difference in affective self-report during left and right amobarbital tests. The major factor distinguishing the wrong way group from the other two appeared to be an asymmetrical distribution of left and right temporal lobe lesions in the former group. In contrast, the factor differentiating the right way group from the no change group appeared to be the relative degree of left hemisphere inactivation during the left hemisphere amobarbital test. The results are discussed not only in terms of their impact on theories of cerebral lateralization for emotion, but also in terms of methodological issues in this field.

Heart rate does not decrease after right hemispheric amobarbital injection

Ten years ago it was reported that the heart rate of 25 patients with different focal epilepsies changed following unilateral hemispheric inactivation by intracarotid amobarbital injection (Wada Test).1 Using mean amobarbital dosages of 126 and 128 mg, the authors showed heart rate increases after left hemisphere inactivation and decreases following right hemisphere inactivation. It was concluded that the results are consistent with differential left/right cerebral hemispheric effects on autonomic function. Within 9 years after publication, this study was cited by 59 publications as reported by the Science Citation Index. However, only one of these studies was aimed at reproducing the results.2 In this study, 32 patients with temporal lobe epilepsy (TLE) and with left hemisphere speech dominance were investigated using 200 mg amobarbital. The patients demonstrated an increase of heart rate immediately after each injection but …

Awareness of and memory for arm weakness during intracarotid sodium amytal testing.

The traditional association between anosognosia for hemiplegia and the right hemisphere was investigated in 31 patients with unilateral temporal lobe pathology during intracarotid sodium amytal testing (ISA) before epilepsy surgery. Recall of arm weakness was examined by questioning at the end of the test, when memory for items presented during the hemiplegia was also examined. Significantly more patients were amnesic for left arm weakness than for right. Amnesia for right arm weakness (and speech arrest) was significantly associated with pathology in the temporal lobe on the non-injected side and with impaired recognition of the memory items. Amnesia for left arm weakness was independent of both. Examination of cases where injection was contralateral to a hemisphere without pathology, and which showed normal memory capacity under ISA conditions, revealed that 87% recalled right arm weakness, but only 22% recalled left arm weakness. Awareness of arm weakness during left hemiplegia was examined in nine patients. Five of them were not aware of the weakness. Three of the four others could not subsequently recall it. By inference from the generally unimpaired recall of right arm weakness, following left hemisphere inactivation by amytal, an intact right hemisphere is capable of both recognizing right arm weakness and mediating its subsequent recall. In contrast, the left hemisphere was aware of left arm weakness only in approximately 50% of cases and even when there had been awareness usually could not mediate its subsequent recall. The suggestion is made that the right hemisphere may have a specific mnestic function for arm weakness, and presumably for hemiplegia, additional to the gnostic function.

Hemisphere Inactivation and Mood-State Changes

Mood-state changes were studied during a sodium Amytal testing procedure in epilepsy patients with unilateral temporal lobe foci. The results showed that inactivation of the left hemisphere, but not the right hemisphere, produced a negative mood state. This decline in mood was not specifically related to side of focus or sex. As expected, the inactivation of either hemisphere also lead to an impairment in memory performance. This impairment was somewhat worse during a left than a right hemisphere inactivation. Furthermore, patients with left hemisphere foci showed a lower memory performance than patients with a right-hemisphere lesion. These results suggest (a) a hemispheric specialization for emotion that underlie changes in mood and (b) a discrepancy between mood states at encoding (during inactivation) and retrieval (after inactivation).

Unilateral cerebral inactivation produces differential left/right heart rate responses

We studied heart rate following unilateral hemispheric inactivation by intracarotid amobarbital in 25 patients undergoing preoperative evaluation for epilepsy surgery. Heart rate increased after left hemisphere inactivation, but decreased following right hemisphere inactivation. The results are consistent with differential left/right cerebral hemispheric effects on autonomic function, and appear related to functional and anatomic asymmetries in both the central and peripheral nervous systems.

Interhemispheric asymmetry of positive emotional reactions in rats.

Interhemispheric asymmetry of positive conditional reactions in rats were investigated, i.e., reactions of drinking need and self-stimulation satisfaction. A successive hemisphere inactivation was performed by potassium spreading depression. Both right and left hemisphere inactivation were shown symmetrically to affect the total quantity of water consumed by the rats until complete thirst satisfaction, i.e., the need magnitude. At different stages of thirst satisfaction, however, interhemispheric asymmetry was observed: when drinking motivation was strong, the right hemisphere dominated, when it was weak the left hemisphere was dominant. Right hemisphere inactivation caused a decrease in the frequency of lateral hypothalamus self-stimulation, whereas with left hemisphere inactivation it increased, which testifies to right hemisphere dominance in self-stimulation reaction. Self-stimulation reaction was also characterized by the asymmetry of lateral hypothalamus nuclei: reactivity of the right nucleus to hemisphere inactivation (decrease or increase in self-stimulation frequency) was more pronounced than that of the left nucleus.

Hemisphere Lateralization of the Extrapolation Reflex

The interhemispheric asymmetry of extrapolation task solution in infant and adult Norway rats (Rattus norvegicus) was investigated. L. V. Krushinsky's technique with a screen was used in combination with hemisphere inactivation by means of spreading depression. It was shown during a short-term adaptation to the experimental conditions, in extrapolation of movement direction at its multiple presentation, that the left hemisphere dominated in infant rats and the right one in adult rats. An additional adaptation caused the change of the asymmetry sign in the adult animals, which is discussed in terms of prevalence of the visuospatial or the rational component of the extrapolation task.

Verbal memory deficits after left temporal lobectomy for epilepsy. Mechanism and intraoperative prediction.

Verbal memory deficits remain a major complication of dominant hemisphere temporal lobectomy for epilepsy. The extent of this deficit was assessed preoperatively and 1 month and 1 year postoperatively with the Wechsler Verbal Memory Scale (WMSV) in 14 adults undergoing left temporal lobectomy. Intraoperative localization of language and verbal memory was also performed by electrical stimulation mapping. The WMSV score decreased an average of 22% at 1 month (13 cases), and 11% at 1 year (10 cases), even though in the majority of cases the medial extent of the resections had been significantly modified as a result of preoperative memory changes in response to intracarotid amobarbital perfusion testing. Memory decline was greater in patients who were not seizure-free, and correlated with the lateral (but not the medial) extent of the resection. The memory deficit could be predicted intraoperatively with 80% accuracy from the relationship of the resection to sites identified by electrical stimulation mapping as essential to naming or input or storage aspects of memory. This technique was applied prospectively in two additional cases with left temporal epileptic foci and complete verbal memory loss with left hemisphere amobarbital inactivation. These resections were tailored to avoid the essential naming and memory sites; the WMSV score increased 1 month postoperatively in both cases. This study identifies a lateral cortical component for verbal memory. Sites essential for that component can be localized intraoperatively with stimulation mapping; when they are spared in a resection, verbal memory deficit following dominant hemisphere temporal lobectomy can be prevented even in high-risk cases.

Simultaneous and sequential processing of information by different hemispheres in animals.

In the experiments on 53 rats, the technique of motion-food conditioned reflexes in combination with unilateral decortication by means of spreading depression was used. Rats were trained in differentiration of geometrical figures united in simultaneous complexes or chain stimuli, presented simultaneously or sequentially. The lateralization of more frequent disruptions was shown to depend, not upon the kind of stimuli used, but upon the character of their presentation. With simultaneous presentation, the greatest disruptions set in after right hemisphere inactivation, but at sequential presentation they were greater as a result of left hemisphere inactivation. It is supposed that animals possess a simultaneous processor in the right hemisphere and a sequential processor in the left one.

Hemisphere specialization of the animal brain for information processing principles.

The experiments were performed on white rats. Different techniques for forming conditioned reflexes were used. Hemisphere cortex inactivation was carried out by means of spreading depression. The right hemisphere was shown to dominate for space perception, simultaneous information processing, concrete characteristics perception, and deductive processing; the left hemisphere was shown to dominate for time perception, successive information processing, abstract characteristics perception, and inductive processing. A hypothesis of induction and deduction being the main factors determining function lateralization in the hemispheres of the animal brain was put forward.

Lateralization of concrete and abstract characteristics analysis in the animal brain.

The experiments were performed on 92 white Wistar rats. Motion-food technique for working out conditioned reflexes was used. The following models were used: reflexes to correlation, transfer of conditioned reflexes, invariant recognition of visual images. Cortex inactivation was achieved by means of spreading depression. Sufficiently crude reflexes to the correlation of geometrical figure area or straight line segment lengths in animal populations were shown to be equally impaired after right and left hemisphere inactivation. In forming conditioned reflexes to the area correlation of some other figures or their accumulations, as well as finer reflexes to the correlation of segment lengths, right hemisphere inactivation led mainly to the impairment of concrete stimuli characteristics, and left hemisphere inactivation to that of abstract ones. Conditioned reflex transfer to other geometrical figures was mainly impaired after left hemisphere inactivation. Invariant recognition of visual images was more impaired after left than after right hemisphere inactivation. The results obtained suggest that in animals the right hemisphere mainly analyses concrete stimuli characteristics, whereas the left one analyses their abstract characteristics.