Neural correlates to seen gaze-direction and head orientation in the macaque monkey amygdala.

Human neuropsychological studies suggest that the amygdala is implicated in social cognition, in which cognition of seen gaze-direction, especially the direct gaze, is essential, and that the perception of gaze direction is modulated by the head orientation of the facial stimuli. However, neural correlates to these issues remain unknown. In the present study, neuronal activity was recorded from the macaque monkey amygdala during performance of a sequential delayed non-matching-to-sample task based on gaze direction. The facial stimuli consisted of two head orientations (frontal; straight to the monkey, profile; 30 degrees rightwards from the front) with different gaze directions (directed toward and averted to the left or right of the monkey). Of the 1091 neurons recorded, 61 responded to more than one facial stimulus. Of these face-responsive neurons, 44 displayed responses selective to the facial stimuli (face neurons). Most amygdalar face neurons discriminated both gaze direction and head orientation, and exhibited a significant interaction between the two types about information. Furthermore, factor analysis on the response magnitudes of the face neurons to the facial stimuli revealed that two factors derived from these facial stimuli were correlated with two head orientations. The overall responses of the face neurons to direct gazes in the profile and frontal faces were significantly larger than that to averted gazes. The results suggest that information of both gaze and head direction is integrated in the amygdala, and that the amygdala is implicated in detection of direct gaze.

Conjunctive effects of reward and behavioral episodes on hippocampal place-differential neurons of rats on a mobile treadmill.

Previous studies reported context (or behavior)-dependent activities of hippocampal place cells, which are suggested to be the neural basis of episodic memory. However, it remains unclear what distinctive items these context-dependent activities encode. We investigated separately the effects of space, locomotion, and episodes with positive/negative reinforcements on activity of place-differential neurons in the hippocampal CA1 area. Rats were placed on a treadmill affixed to a motion stage translocated along a figure 8-shaped track. The track could be navigated by two different routes that shared a common central stem. The stage was paused at the start and end of the routes, where conditioned response tasks with different reinforcements were imposed. As the rats passed the common central stem, some neurons fired differently depending on the route. Comparison of hippocampal spatial firing patterns across different conditions with and without treadmill operation and/or the tasks indicated that these route-dependent spatial firing patterns were sensitive to locomotion, the tasks, and vestibular sensation or visual cues such as optic flow. The results suggest that external sensory inputs, path integration, and reinforcement context are all integrated in the hippocampus, which might provide the neural basis of episodic memory.

[Effects of lesions in the central nucleus and lateral nucleus of the amygdala on fear conditioning with a visual conditioned stimulus in rats].

Lesions in the central nucleus or lateral nucleus of the amygdala have been known to interfere with the acquisition of fear conditioning when a sound is used as a conditioned stimulus (CS). The present study examined whether or not a similar interference would occur with a visual CS. Seven rats with lesions in the central nucleus (AMY-C group), 8 with lesions in the lateral nucleus (AMY-L group), and 16 unoperated control rats were trained using a visual CS (25 W light, 3.7 s duration) paired with footshock (1.0 mA, 0.5 s). The behavioral index of fear conditioning was a potentiation of startle reflex in the presence of CS. All control rats and AMY-L group showed the potentiation, but AMY-C group did not. These results suggest that the lateral nucleus of the amygdala may not be involved in fear conditioning to a visual CS. It is possible that each modality of CS has a specific pathway to the central nucleus of the amygdala to mediate fear conditioning.

Effects of hexose infusion with insulin and of additional epinephrtine injection on the levels of serum potassium and blood glucose in dogs.

The hypokalemic response was roughly proportional to the dose of insulin. The hypokalemia due to adding insulin to galactose or fructose loading was slightly greater than that with insulin and glucose or mannose loading, suggesting a hexose stereospecificity of the response. When epinephrine (13.6 nmol/kg, i.v.) was given after one of the hexoses plus insulin, the hyperkalemia with glucose and galactose was 2.5-3 mEq/l, about twice that due to fructose or mannose. The hyperglycemia was about 2 mmol/l for glucose, 1 mmol/l for galactose, mannose, fructose, and ouabain with glucose, and 0.25 mmol/l for phloridzin with glucose. Addition of epinephrine, isoproterenol, and cAMP caused a significant depression of Na+,K+-ATPase activity in rat liver (P < 0.01) but the addition of insulin did not. These results show that there was a relation between the levels of blood glucose and serum potassium after an insulin-containing hexose infusion and that membrane permeability was stereospecific.