Associative learning in premature hydranencephalic and normal twins.

A hydranencephalic infant lacking cerebral hemispheres and a normal twin were tested for associative learning. After repeated trials in which two stimuli were temporally paired, test trials were given in which the second stimulus was omitted. Cardiac orienting responses to stimulus omission indicated that learning had taken place in both infants.

Computer simulations of neural information processing and the schizophrenia-mania dichotomy.

Recent developments in artificial intelligence use computer simulations of complex neural systems to model associative memory and gestalt-seeking during cognition. Perturbations imposed on such computer simulations caused catastrophic breakdowns of neural functioning. The resulting cognitive disturbances assumed two forms, one "schizophreniclike" and the other "maniclike." The former was induced by memory overload and resulted in misperceptions, loose associations, and also parasitic processing states that pathologically controlled the flow of associations. The latter was caused by increased randomness of neural activity, which induced "jumps" from one gestalt to another. The relationship between this differential model of psychotic disturbances and other studies of schizophrenia and mania were explored.

Association and commissural fiber systems of the olfactory cortex of the rat.

The association and commissural fiber systems arising in the olfactory cortical areas caudal to the olfactory peduncle (the piriform cortex, nucleus of the lateral olfactory tract, anterior cortical nucleus of the amygdala, periamygdaloid cortex and entorhinal cortex) have been studied utilizing horseradish peroxidase as both an anterograde and a retrograde axonal tracer. In the piriform cortex two sublaminae within layer II (IIa and IIb) layer III have been found to give rise to distinctly different projections. Retrograde cell labeling experiments indicate that the association fiber projection from layer IIb is predominatnly caudally directed, while the projection from layer III is predominantly rostrally directed. Cells in layer IIa project heavily to areas both caudal and rostral to the piriform cortex. The commissural fibers from the piriform cortex are largely restricted in their origin to layer IIb of the anterior part of the piriform cortex and in their termination on the contralteral side to the posterior part of the piriform cortex and adjacent olfactory cortical areas. A projection to the olfactory bulb has also been found to arise from cells in layers IIb and III of the ipsilateral piriform cortex, but not in layer IIa. In addition to those from the piriform cortex, association projections have also been found from other olfactory cortical areas. The nucleus of the lateral olfactory tract has a heavy bilateral projection to the medial part of the anterior piriform cortex and the lateral part of the olfactory tubercle (as well as a lighter projection to the olfactory bulb); both the anterior cortical nucleus of the amygdala and the periamygdaloid cortex project ipsilaterally to several olfactory cortical areas. The entorhinal cortex has been found to project to the medial parts of the olfactory tubercle and the olfactory peduncle. The olfactory tubercle is the only olfactory cortical area from which no association fiber systems (instrinsic or extrinsic) have been found to originate. A broad topographic organization exists in the distribution of the fibers from several of the olfactory areas. This is most obvious in the anterior part of the olfactory cortex, in which fibers from the more rostral areas (the anterior olfactory nucleus and the anterior piriform cortex) terminate in regions near the lateral olfactory tract, while those from more caudal areas (the posterior piriform cortex and the entorhinal cortex) terminate in areas further removed, both laterally and medially, from the tract. Projection to olfactory areas from the hypothalamus, thalamus, diagonal band, and biogenic amine cell groups have been briefly described.

Effect of 5,7-dihydroxytryptamine on the food-aversive conditioning in the snail Helix lucorum L.

The effects of 5,7-dihydroxytryptamine (5,7-DHT), a drug which selectively ablates serotonergic terminals, were examined on acquisition of food-aversive conditioned reflex in the snail Helix lucorum. The percent of feeding reactions decreased from 80 to 15% in the conditioned group of animals after 5-8 pairings of food and electric shock. The behavioral performance of 5,7-DHT-injected animals after the same training session coincided with the data received from the unpaired control group: the percent of feeding reactions remained the same as before the training. Conditioning was carried out on the semi-intact 'lip-CNS' preparations as well. Intracellular recordings from the neurons responding to the withdrawal reaction confirmed the results of the behavioral experiments. Elaboration of associative changes was effective on preparations made from normal snails, whereas no changes were noted in 5,7-DHT-treated and pseudoconditioned animals. In 5,7-DHT-treated animals some components of the feeding behavior and withdrawal reaction changed as well. The appetitive phase duration of feeding lengthened significantly, moreover the sensitization of the withdrawal reaction evoked by rhythmic tactile stimulation disappeared in preparations made from drug-treated snails.

A case of visual agnosia showing a disorder of pre-semantic visual classification.

A case (J.R.) of associative visual agnosia (loss of meaning for visually presented objects without any serious sensory disorder) is reported. When asked to match a given name to sample the patient made both visual and semantic errors. Whereas semantic errors were reduced by priming, visual errors were intractable. It is argued that there is a disorder at the stage of pre-semantic abstraction, similar to that postulated elsewhere for some cases of deep dyslexia, contributing to the agnosia.

Intrinsic connections and cytoarchitectonic data of the frontal association cortex in the dog.

Organization of intrinsic connections of the frontal association cortex (FAC) in dogs was studied using retrograde HRP-transport method. For cytoarchitectonic observations and measurements of thickness of the cortex and its particular layers, additional sections stained with Nissl method were examined. Organization of intrinsic connections showed that within the dog's FAC two main cortical zones could be distinguished - the dorsal and the ventral one. The dorsal zone involves dorsally situated areas on the lateral and medial aspects of the hemisphere, which belong to the prefrontal and premotor regions. The vientral zone consists only of prefrontal areas situated ventrally on both aspects of the hemisphere. Each of the zones is characterized by strong mutual intrinsic connections and weak connections with the other zone. At the border there is a transitional area in which connections from both dorsal and ventral zones overlap. The cytoarchitectonic observations indicated that the dorsal and ventral zones can be distinguished in the central and caudal, but not in the rostral FAC subregion. The dorsal zone is characterized by considerable thickness of the cortex, cortical layers III and V, and the presence in these layers of scattered, large pyramidal neurons. The ventral zone has thinner cortex and layers III and V, and their pyramidal neurons are more uniform in size. In none of the zones clearly defined granular layer IV was observed.

Associative strength level and retrieval inhibition in semantic memory.

In a series of investigations, E. F. Loftus (1973; G. R. Loftus & E. F. Loftus, 1974; E. F. Loftus, Senders, & Turkletaub, 1974) discovered that the latency of item retrieval from a semantic category was reduced if it immediately followed an earlier retrieval from the same category, a phenomenon attributed to spreading activation. Subsequently, Brown (1981) discovered an increase in latency across extended retrievals from a single semantic category. The present investigation followed up this finding by comparing exemplars that varied in strength of association to the category name. The probability of obtaining inhibition (longer latencies and increased errors) was inversely related to the associative strength of the exemplars. The results suggest that low-strength category associates build up inhibition more rapidly because they accrue situational strength relatively more rapidly than high-strength associates.

Lateral differences for person perception: effects of task on visual processing of handwriting.

Sergent and Bindra suggested that identification of faces using few different stimuli engages mainly the left hemisphere and, conversely, that discrimination of faces using more stimuli engages mainly the right hemisphere. The present study examined whether this suggestion holds for the perception of handwriting which, like faces, authorizes the perception of "persons". Normal adults were presented stimuli consisting of a word written in various hands, laterally displayed for 180 msec. Exp. 1 (identification) was conducted with 8 subjects, who were asked to identify (push-button) four different stimuli by means of an associated first name. Exp. 2 (discrimination) was conducted with 16 subjects who were asked to make same/different judgments between a central stimulus and a lateral one under three experimental conditions, normal, mirror-reversed, and inverted presentations of both members of the pair. The results suggest that the direction of asymmetry depends more on the amount of stimuli than on the task and that familiarity with the stimuli is an important variable.

[Conditioned slow negative potential during learning motor habits of different complexity]. / Uslovnyi medlennyi otritsatel'nyi potentsial pri obuchenii dvigatel'nym navykam razlichnoi slozhnosti

CSNP dynamics was studied on 13 subjects in three experimental situations: 1) In combinations of acoustic and photic stimuli without performance of movements; 2) During the pressing of the palm at the moment of the anticipated photic stimulus; 3) After preliminary switching off of the photic stimulus. In the first situation CSNP does not appear; in the second, it has a maximum amplitude at the unitial stages of movement elaboration at a definite time interval, and in the third, CSNP amplitude does not decrease during 300 stimuli combinations. The CSNP amplitude, configuration and stability depend on the degree of complexity of the motor task. It has been assumed that CSNP reflects a non-specific activation of frontal and central parts of the human brain, against the background of which integration of sensory information takes place as well as the formation of a temporal program of the subsequent motor act.

[Statistical characteristics of evoked responses to light in analysis of intercentral relationships]. / Statisticheskie kharakteristiki vyzvannykh otvetov na svet v analize mezhtsentral'nykh otnoshenii

In acute experiments on unanaesthetized cats immobilized with listenon, a study was made ofthe variability and interdependence of evoked responses to photic stimulation in the thalamo-cortical formations of the visual projection and the associative systems: the lateral geniculate body, pulvinar and the visual and parietal associative areas of the cerebral cortex. It has been shown that the variation coefficient of the amplitude from the maximum of the positive to the maximum of the negative oscillations in the parietal cortex statistically significantly exceeds the one in the lateral geniculate body and the projection cortex. Coefficients of paired correlation of evoked potentials' amplitudes to light more frequently reach significant levels for pairs consisting of one level formations, cortical or thalamic, than for pairs including formations of different levels.

[Effect of the motor cortex on heterogeneous afferent flows in the mediodorsal nucleus of the thalamus]. / Vliianie motornoi oblasti kory na geterogennye afferentnye potoki v mediodorzal'nom iadre talamusa.

In experiments carried out on cats anaesthetized with Nembutal evoked potentials were recorded in the thalamic mediodorsal (MD) nucleus and in the projection and motor cortical areas with local cooling of the latter and the use of either single or paired stimuli of the same or different modalities. Visual and somatic excitatory inflows to the MD have been established, involving signals of specific and reticular genesis. Coming by separate ways they form isolated populations of neurones in the MD. A facilitating modulating influence of MD has been defined on the realization of afferent bursts produced in the motor cortex by visual and, particularly, somatic stimuli. It was found that in spite of its polyfunctionality, the motor cortex specifically influences heterogeneous inflows to the MD, exerting a more intensive and different action on the somatic afferentation as compared with the visual one. It is assumed that the specific and direct influence of the motor cortex on these impulses is exercised due to a functional subdivision of its corticofugal pathway into separate subsystems.

[Consciousness and evoked cerebral cortical electrical activity]. / Soznanie i vyzvannaia élektricheskaia aktivnost' kory bol'shikh polusharii.

The analysis of the late positive wave (component P300) of an averaged evoked potential, recorded to visual stimuli in different experimental situations has shown that local activation of the cerebral cortex during conscious experience (Pavlovian "light spot") is of a dynamic nature and is determined by signal significance of stimuli and predominant voluntary activity. In cases when it is necessary to decide on the choice of reaction anterior areas of neocortex are activated. If the function of perception is dominating the local activation essentially occurs in corresponding cortical area at which the perceived stimulus is timed. The cortico-thalamo-cortical mechanism of focused attention and its role in providing for conscious human experience is discussed.

[Interaction between spindles evoked by electric stimulation of different regions of the cerebral cortex]. / K vzaimodistviiu vereten, vyzvannykh élektricheskim razdrazheniem raznykh oblastei kory bol'shikh polusharii golovnogo mozga

In unanesthetized immobilized cats, under repeated administration of small doses of nembutal (2-3 mg/kg), connections between the projection and the parietal associatition cortical areas was studied as well as the interaction between spindles elicited by stimulation of these areas. Stimulation of the primary sensory areas (auditory or somatosensory) was shown to be able to elicit spindles not only in the stimulated area but in the association cortex too. This latter spindle, being kind of induced from the sensory areas, interacts with the spindles elicited by the direct electrical stimulation on the association cortex.

[Evoked activity of cat association cortex neurons in different sleep stages]. / Vyzvannaia aktivnost' neironov assotsiativnoi kory kotiat v raznye fazy sna

Evoked activity of neurons in the parietal associative cortex in response to adequate and electric stimulations of the thalamic radiation fibers was studied during different phases of sleep. The number of responding neurons decreased during slow--wave and, particularly, during paradoxical sleep. With transition from phase to phase, responsiveness changed mainly in polysensory neurons which gave variable responses with long latencies. Mechanisms of change of responsiveness during the two phases appear to be different. Reliable increase of the inhibitory pause in responses during slow-wave sleep and its decrease during paradoxical sleep may indicate a strengthening of mechanisms of reciprocal inhibition during the first phase, and their weakening during the second phase.

[Heterosensory interaction in neocortical neurons of the hedgehog, Erinaceus europaeus]. / Geterosensornoe vzaimodeistvie na neironakh neokorteksa ezha Erinaceus europaeus.

Reactions of neurons in different areas have been investigated in the hedgehog cortex by means of the microelectrode technique. A wide dispersion of afferent inputs was shown over the whole neocortex, alongside with the existence of definite projection foci of appropriate modalities. In the specific projection zones the conditioning heterosensory stimulation did not influence the onset of the response of the testing specific stimulus. Blocking of responses was observed in the so-called "associative" area, irrespectively of the mode of the conditioning and testing stimulation. It is suggested that the onset of responses by the specific projection zones to other stimuli depends on the specific impulsation irradiation to the specific projection pathways. Reciprocal heterosensory blocking in the "associative" zone may indicate the existence of an integrative formation in the hedgehog thalamus, possessing its own projection to the neocortex.