Birger R. Kaada

Stimulation and Regional Ablation of the Amygdaloid Complex with Reference to Functional Representations

Stimulation and ablation of the amygdaloid nuclear complex result in a variety of somatic, visceral, endocrine and behavioral effects. Since this brain area is a very heterogeneous structure, with a number of rather distinct subdivisions, and since differences in structure obviously implies functional differences, it is reasonable that attempts have been made to correlate structure and patterns of responses.

Functional localization within the amygdaloid complex in the cat.

Abstract 1. 1. The behavior, somatomotor and autonomic effects observed from stimulation of 182 electrode sites in the amygdala (149 in unanesthetized cats) are reported. The results, together with a closer analysis of the data published by other authors, indicate a definite topographic organization of different functions within the amygdala, although with some overlapping. Each type of response is discussed under the various sections. 2. 2. Behavior “attention” (fig. 1) in conjunction with EEG “desynchronization” (fig. 2) is related to the basolateral division of the amygdaloid complex. The responsive zone can be traced medially through the region of the central nucleus into the internal capsule. This extension appears to correspond to the “c-bundle” of Fox (fig. 3 and 4). 3. 3. Fear (flight) and anger are produced from two separate areas running approximately parallel within the “attention” zone from the basolateral nuclei and into the internal capsule and brain stem (fig. 5 and 6). 4. 4. Various somatomotor (sniffing, licking, chewing, facial contractions) and autonomic e effects (salivation, respiration, pupillodilatation, micturition, defecation, piloerection) are elicited from different portions of the amygdaloid complex (fig. 7, 8 and 9). 5. 5. The pathways for some of these reactions are briefly discussed.

Effects of hippocampal lesions on maze learning and retention in rats.

Abstract Clinical observations suggest that bilateral damage of the hippocampal region and fornix may result in severe disturbances of recent memory. Experiments were undertaken to determine whether hippocampal and fornical lesions in rats have deleterious effects on maze learning and retention. A fourteen-choice mutiple-T alley maze was employed. The effect on postoperative initial learning was studied in fifty-two rats. One group of animals sustained bilateral and another group unilateral hippocampal or fornical lesions. A third group served as operated controls and received lesions in the same neocortical areas as the hippocampectomized animals. A fourth group of one hundred four rats were used as nonoperated normal controls. The animals with hippocampal or fornical lesions showed a significantly defective maze learning compared with the operated and nonoperated controls in terms of total errors and time required to run the maze. Deficit in maze performance also followed removal of the mamillary bodies. Thirty-eight rats were used in retention experiments and sustained either bilateral or unilateral hippocampal lesions, or removals of the neocortex overlying the hippocampus. All animals in this series were incompletely trained preoperatively and retrained postoperatively. The hippocampectomized rats suffered significant impairment in maze retention and relearning compared with the operated controls. It was concluded that lesions of the hippocampus, fornix, and mamillary bodies seem to interfere with maze learning and retention, when incompletely trained preoperatively. The data obtained do not allow any conclusions as to how these structures are involved in learning and retention, neither as to their relative importance compared with other brain structures like neocortex or thalamus, both of which are previously known to influence learning and retention.

Differential effects of hippocampal lesions on maze and passive avoidance learning in rats

Abstract In a previous study it was shown that bilateral hippocampal lesions in rats have a deleterious effect on performance in a fourteen-choice multiple-T alley maze. Lashley had not observed such an effect with his maze III. We suspected that different types of mazes possibly do not have the same ability to differentiate animals with hippocampal lesions from normal ones. In the present study, the Hebb-Williams maze, which consists of a battery of twelve different maze patterns, was used. The over-all score in this test was found to differentiate clearly between rats with hippocampal lesions and normal animals. Furthermore, some maze patterns were found to differentiate the group with bilateral hippocampal lesions from normal animals better than other maze patterns. A test of passive avoidance was included in the experiments to provide an independent measure of “emotional” changes. None of the animals with hippocampal lesions deviated significantly from the normal rats on this test. On the other hand, a deficiency in passive avoidance behavior was produced in rats with bilateral lesions in the septal and insular areas. These observations confirm our previous findings that maze learning and passive avoidance learning are dependent on different brain structures.

Behavior “attention” and fear induced by cortical stimulation in the cat☆

Abstract 1. 1. The cerebral cortical areas have been determined from which a behavior “attention” response can be induced by stimulation in the unanesthetized cat. Three components may be distinguished in this behavior pattern: (i) arrest of all ongoing spontaneous movements; (ii) increased alertness; and (iii) orienting movements towards the contralateral side (fig. 1). The response is probably identical with the “orienting reflex” described by Pavlov. 2. 2. The responsive areas include: (i) the cortex of the medial frontal surface, the cingulate and hippocampal gyri; (ii) the intermediate lateral frontal cortex; (iii) a large temporo-occipital field; (iv) the orbito-insular-temporal polar region; and (v) a weaker parietal field. These cortical zones correspond to those from which a generalized electrocortical activation have been elicited in the cat and monkey (fig. 3 A-B and 4 A-B). Cytoarchitectonically, they appear to be related to the “limitropic” type of association cortex (fig. 4E-F). 3. 3. The positive areas coincide with those previously known to produce inhibition of spontaneous movements, various autonomic effects and contraversion (fig. 3 C-D and 4 C-D). These responses, obtained under anesthesia, are interpreted as parts of the complex behavior “attention” pattern evoked in the unanesthetized animal. 4. 4. Fear resulted from stimulation of the cingulate and temporo-occipital cortex. Its relation to fear in epileptic seizures is discussed.

Subcortical structures mediating the attention response induced by amygdala stimulation

Electrical stimulation of the amygdaloid nuclear complex in unanesthetized freely moving cats elicits a characteristic searching or attention response. Attempts have been made by combined stimulation-ablation techniques to determine the subcortical structures through which this response is mediated. The only lesion which eliminated the attention response was an almost complete vertical circumcision of the amygdala with interruption of the connections irradiating in the anteromedial, medial, and posteromedial directions. Selective section of any of these connections by lesions placed either anteromedially, medially, or posteromedially to the amygdala, in various combinations, were ineffective. It is concluded that the attention response is mediated through several pathways to widespread subcortical areas. Bilateral lesions of various subcortical nuclei onto which the amygdala is known to project did not abolish the attention response. Such lesions destroyed in various combinations the almost entire thalamus (including all mid-line and intralaminar nuclei), the subthalamus, extensive parts of the hypothalamus (including nucleus ventromedialis), and the preoptic area, the septal nuclei, the reticular formation, and the rostral half of the periaquaeductal gray matter of the midbrain, the pretectal area, the superior colliculi, the habenula, the substantia nigra, and the red nuclei. It is suggested that the amygdaloid attention response is mediated through several of these subcortical areas which could not be eliminated in toto in one and the same animal, because such extensive lesions were not compatible with survival.

Deep coma associated with desynchronization in EEG

Abstract Previously a few patients have been described in which a comatose state following brain lesions has not been correlated with organized slow waves in the EEG but with a normal activity as seen in the waking or alert state. A similar case with anatomical control is presented. In all these patients the injury has involved the middle and rostral portion of the pons. The observations are discussed in relation to recent neurophysiological findings.

Locomotor, avoidance and maze behavior in rats with the dorsal fornix transected ☆

Transection of the dorsal fornix bundle in rats resulted in impaired maze learning, while the behavior in open field, passive avoidance and spontaneous alternation test was unchanged. The results are discussed in terms of an association deficit. It is concluded that the dorsal fornix is probably not to be regarded as part of the hippocampal output system.

Generalized electrocortical activation by cortical stimulation in the cat

Abstract 1. 1. In the cat, the cerebral cortical areas have been determined from which on electrical stimulation a generalized electrocortical activation (desynchronization) can be elicited (fig. 1). 2. 2. Positive sites were located in (i) the medial frontal cortex and the cingulate and hippocampal gyri; (ii) the intermediate lateral frontal cortex; (iii) the temporo-occipital cortex; (iv) the orbito-insulo-temporal polar region; and (v) the parietal cortex. 3. 3. The responsive areas correspond to those from which a behavior “attention” response, various autonomic effects, and inhibition of spontaneous movements can be obtained. Through projections to the brain stem or thalamic reticular areas these cortical fields probably contribute to the initiation and maintenance of wakefulness and directed attention.

Failure to modulate autonomic reflex discharge by hippocampal stimulation in rabbits

Abstract This study investigated the possibility that the hippocampus exerts a modulating influence on autonomic reflexes. Electrical stimulation of the dorsal and ventral hippocampus of unanaesthetized rabbits had no effect on an olfactory-trigeminal induced inhibition of respiration and heart rate. Neither was a conditioned fear induced acceleration of respiration and heart rate influenced by hippocampal stimulation. Even prolonged electrical seizure discharges in the hippocampus did not alter, or only slightly influenced, normal or the induced autonomic changes. Hippocampal stimulation did evoke weak autonomic changes as part of an arousal reaction to which however the animals became quickly habituated.