Abilities and neural mechanisms underlying AB performance.

Schacter, Moscovitch, Tulving, McLachlan, and Freedman propose that infants may make the AB error because of immaturity of the memory system damaged in amnesia (e.g., the hippocampus). They contrast this with the proposal that infants may make the AB error because of immaturity of the frontal lobe system (Diamond; Diamond & Goldman-Rakic). Schacter et al.'s choice of subjects, however, did not permit a test of these 2 proposals, and characteristics of their task, such as length of delay, make comparison with infants difficult. Schacter et al. discuss sensitivity to proactive interference as a possible explanation for the AB error, but sensitivity to PI is more closely associated with frontal lobe damage than with amnesia. Schacter et al. associate perseveration with immaturity or damage to the frontal lobe; it is suggested here that this is better characterized as lack of inhibitory control. Tasks that are most likely to require frontal cortex function are those that demand both short-term memory and inhibitory control. AB is an excellent example of such a task.

Spontaneous alternation and exploration in staggerer mutant mice.

Staggerer mutant mice were found to be less active in terms of motor activity in a maze, hole poking and rearing. Staggerer mutant mice also showed a lack of spontaneous alternation in both 2-trial and 4-trial tests. A lack of spontaneous alternation in this mutant may be due to a deficit in response inhibition or in spatial orientation, similar to that of animals with limbic lesions.

Psychoneurogenic stress influences upon retention of an inhibitory avoidance response in the rat.

Hormones and peptides involved in the response of an organism to stress play a modulating role in learning and memory processes. We studied whether psychoneurogenic stressors such as sound stimulation or novelty influence retention of an inhibitory avoidance response. An impairing effect on retention was observed when these stressors were applied shortly after the acquisition trial, but not after a 3-h delay. However, sound stimulation and novelty applied shortly before the retention test may facilitate retention behavior. It is suggested that the effect of psychoneurogenic stressors on retention behavior may be linked to influences on consolidation and retrieval processes mediated through the neurohumoral response of the organism to stress.

Psychophysiological aspects of depressive syndromes.

Compared to 30 healthy controls, 59 drug free patients with primary major depression exhibited significantly higher rates of heart beat, respiration, and eye blinking; longer simple and associative reaction times; fewer spontaneous fluctuations of skin resistance, a lower salivation rate, a faster habituation rate of skin resistance orienting response, and a smaller CNV area in the EEG. Skin resistance level, speech pause time, N1P2 amplitudes of acoustically evoked potentials and the postimperative negative variation (PINV) in the EEG did not differ between groups. All deviations are nosologically unspecific; they can be regarded as signs of overarousal, as deficits, or as the result of protective inhibition. In all subjects the investigation was repeated twice, while the patients were treated with either amitriptyline or oxaprotiline, repetition of measurement influenced several variables, but most patient/control differences remained unaffected--irrespective of the drug applied.

Effects of attending selectively to the spatial position of reflex-eliciting and reflex-modulating stimuli.

The question of whether automatic, sensory processes can be modified by selectively directing attention to stimuli was addressed by comparing effects on brainstem reflexes that share a common efferent pathway but have distinct afferent limbs. Subjects judged the duration of brief but intense blink-eliciting tones (Experiment 1) or weak tones preceding a blink-eliciting air puff at interstimulus intervals producing blink inhibition (Experiment 2). Tones occurred unpredictably at left, right, or midline loci; designation of the target location varied across blocks of trials. Latency of blinks to lateralized blink-eliciting targets was facilitated selectively, and the magnitude of blinks evoked by air puff following lateralized prestimulus targets was inhibited selectively. There was no evidence for a midline selective effect. Results appear to support a preset differential processing of stimuli in sensory pathways at low, possibly subcortical, levels and the consequent modification of obligatory, automatic processes.

Inhibition of the eyeblink reflex in the human infant.

In human adults the eyeblink elicited by a given stimulus can be inhibited if that stimulus is preceded by another stimulus at an appropriate lead interval. In the present work, pairs of eyeblink-eliciting stimuli separated by 300-1200 msec were presented to sleeping preterm and full-term infants as well as to adults. Preterm infants did not exhibit reliable inhibition at any interval. Full-term infants did so, but they required longer interstimulus intervals than were needed for inhibition in the adult subjects. Results imply that the neural systems that mediate reflex inhibition are functional at birth, but that they are relatively slow to act.

[Role of the midbrain central gray substance in the performance of a conditioned reflex]. / Rol' tsentral'nogo serogo veshchestva srednego mozga v osushchestvlenii uslovnogo refleksa.

The conditional placing reflex was studied in chronic experiments on cats. Neuronal activity of the midbrain periaqueductal grey matter was recorded under conditions of extinction, differentiation and conditional inhibition. Neuronal reactions preceded the conditioned and voluntary movements by 400-800 ms and lasted for 1-2 s in 69 units from total numbers 182 (36.7%). This reactions appeared 200 ms earlier than corresponding neuronal reactions of the motor cortex. 58 neurons (30.9%) were excited by auditory stimuli with latencies 10-50 ms for 2-6 s. 19 neurons (10.1%) were activated by auditory stimuli and conditioned movement. Responses to isolated auditory stimulation were absent in 42 neurons (22.3%), but some of the neurons showed long-lasting (minutes) changes of the background activity under repeated conditioned stimulation. The extinction, differentiation and conditioned inhibition caused specific changes in activity of different neuronal groups. A conclusion is made that the periaqueductal grey matter participated in reflex performance as well as in its inhibition. The functional independence of the first and second neuronal groups in extinction and restoration of conditional reflex is shown.

Hippocampectomy selectively disrupts discrimination reversal conditioning of the rabbit nictitating membrane response.

The effects of hippocampal lesions were tested on two-tone discrimination reversal conditioning of the rabbit nictitating membrane response. Results showed that hippocampectomized animals learned the initial two-tone discrimination at rates equivalent to operated control animals and animals with neocortical lesions. During reversal conditioning, however, animals with hippocampal lesions were severely impaired relative to both other groups. Neocortical lesions were without effect on reversal learning. An additional study revealed that the hippocampectomized animals' failure at reversal could not be attributed to a lesion-induced increased resistance to extinction. Results are discussed with respect to several theories of hippocampal function, and with respect to changes in the activity of hippocampal pyramidal neurons which occur during classical conditioning of the nictitating membrane response.

Modulation of behavioral inhibition in appetitive extinction following manipulation of adrenal steroids in rats: implications for involvement of the hippocampus.

Corticosterone, the principal glucocorticoid in the rat, binds selectively to the CA1 pyramidal neurons of the hippocampus where the hormone has been demonstrated to exert a moderate chronic suppression of spontaneous activity. In the first experiment of the current study, the functional behavioral significance of this hormone--brain interaction was investigated in the extinction of an appetitive runway response in normal rats and those with lesions of the hippocampus. During extinction, half of the animals in each group were given daily subcutaneous injections of corticosterone. Whie the classical retardation effect of hippocampal lesions on appetitive extinction was replicated, hormone treatment was without effect in normal or hippocampally damaged subjects. The absence of a hormone effect in normals was primarily attributed to a saturated limited-binding system operating in the normal animal. Experiment 2 tested this notion, repeating the first experiment, with adrenal-ectomized (ADX), ADX + corticosterone replacement, and normal groups of animals. Adrenalectomy produced a striking facilitation of extinction which was speculated to be the result of a hyperactive inhibitory neural organ free from an inhibitory endocrine feedback. Corticosterone treatment normalized the progress of extinction in ADX animals, providing support for the afore-mentioned speculation. In the normal animal, it appears that a stress-induced surge in hormone level interacts with a limited-capacity neural binding to produce a transient dynamic range of behavioral disinhibition, perhaps promoting persistence during initial stages of frustrative nonreward in moderate stress tasks.

[Mechanism of internal inhibition (role of the sympathetic nervous system in sleep phenomena)]. / K voprosu o mekhanizme vnutrennego tormozheniia (po dannym o roli simpaticheskoi nervnoi sistemy v iavleniiakh sna)

It has been shown on cats that the role of the sympathetic nervous system in sleep phenomena is of an adaptive nature and is effected through chain neurohormonal reactions in which adrenaline possessing a two-phase action plays a major part: it induces excitation followed by sleep. Sleep is regarded as a variety of internal inhibition, elaborated as an adaptive reaction to the changing conditions of environment, which later becomes a behavioral reaction.

[Slow potentials and the impulse activity of cerebral cortex neurons following elaboration of internal inhibition]. / Medlennye potentsialy i impul'snaia aktivnost' neironov kory bol'shogo mozga pri vyrabotke vnutrennego tormozheniia

The development of all studied kinds of internal inhibition in rabbits is accompanied by an enhanced phasic state, alternation of activation and inhibition in the responses of the visual area neurones, and enhanced late components of evoked potentials to flashes. During further intensification of inhibition, generalized polyrhythmic potential oscillations develop, which are in correspondence with chaotic or irregular group discharges of units in the visual and sensorimotor cortical areas, separated by inhibitory pauses. It has been concluded that enhanced hyperpolarization plays a considerable part in the development of internal inhibition; it may be local, predominantly in the conditioned stimulus analyser, or generalized in the case of a stronger inhibition comprising many brain structures.

Food-deprivation-induced behavioral arousal: mediation by hypothalamus and amygdala.

Electrolytic lesions of the basomedial hypothalamus eliminated food-deprivation-induced stabilimeter activity in rats that were prevented from becoming obese. Knife cuts lateral to the basomedial area (separating the medial and lateral hypothalamus) potentiated this activity, as did transections posterior to the basomedial region. Anterior transections (between anterior and medial hypothalamus), however, eliminated the effect. Lesions of the stria terminalis and amygdala likewise abolished deprivation-induced locomotor activity, but elevated ab-lib activity to a level comparable with that after deprivation in intact animals. Animals with combined basomedial-stria terminalis lesions behaved like animals with basomedial lesions. These results suggest that food-deprivation-induced locomotor activity in stabilimeter cages is due to a disinhibition of the basomedial hypothalamus by the amygdala via the stria terminalis.

Acoustic startle reflexes in the rat during consummatory behavior.

Auditory startle reflexes were elicited in thirsty rats when they were drinking water or were between drinking boutsmthe reaction was greater during drinking, this enhancement developing over the first few seconds after drinking onset. The startle reaction was lowest immediately after the termination of drinking. Reflex enhancement was reduced when thirsty rats drank milk rather than the more preferred water. The reflex was smaller with increased water deprivation, but enhancement produced by drinking was apparent at all levels of deprivation studied, satiety to 4-days deprivation. The inhibitory effect of a preliminary stimulus was not affected by consummatory behavior. Attention is drawn to suggestive parallels between these behavioral effects and other consequences of consummatory activity, primarily having to do with electrophysiological events and arousal processes