Effect of verbal reinforcement on evoked cortical activity

Adult healthy subjects did not manifest any difference in latency and amplitude of the wave P300 elicited by a positive ("good") and negative ("error") reinforcing stimuli. After the negative reinforcement, the P300 wave amplitude decreases in response to the standard stimulus (light bars) and increases to a lesser degree in response to test stimuli (the same bars but presented with different pauses). In the processes of learning to assess time microintervals in comparison with the standard, the latency of wave P300 to the test stimuli shortens. It is suggested that formation and consolidation of feedback connection elaborated with the participation of a reinforcing verbal stimulus constitute the physiological basis for learning of comparative assessment of time microintervals.     

Network dynamics and synchronous activity in cultured cortical neurons

Neurons extracted from specific areas of the Central Nervous System (CNS), such as the hippocampus, the cortex and the spinal cord, can be cultured in vitro and coupled with a micro-electrode array (MEA) for months. After a few days, neurons connect each other with functionally active synapses, forming a random network and displaying spontaneous electrophysiological activity. In spite of their simplified level of organization, they represent an useful framework to study general information processing properties and specific basic learning mechanisms in the nervous system. These experimental preparations show patterns of collective rhythmic activity characterized by burst and spike firing. The patterns of electrophysiological activity may change as a consequence of external stimulation (i.e., chemical and/or electrical inputs) and by partly modifying the "randomness" of the network architecture (i.e., confining neuronal sub-populations in clusters with micro-machined barriers). In particular we investigated how the spontaneous rhythmic and synchronous activity can be modulated or drastically changed by focal electrical stimulation, pharmacological manipulation and network segregation. Our results show that burst firing and global synchronization can be enhanced or reduced; and that the degree of synchronous activity in the network can be characterized by simple parameters such as cross-correlation on burst events.     

The role of the thalamic ventrolateral nucleus in the cortical effect on the activity of vestibular neurons

Electrocoagulation of lateral vestibular nucleus (NVL) reduces inhibitory effect of the motor and somatosensory areas and enhances the inhibitory effect of limbic, vestibular, and orbital cortical areas. Facilitating effect was enhanced by electrostimulation of the motor area and reduced by the stimulation of other cortical areas. Following the coagulation of the NVL, the ascending afferent flow to the cortex seems to be reduced. This results in diminishing of the cortical neurones tone and readjusts the descending influences upon the NVL neurones activity.     

An information-theoretic approach to curiosity-driven reinforcement learning

We provide a fresh look at the problem of exploration in reinforcement learning, drawing on ideas from information theory. First, we show that Boltzmann-style exploration, one of the main exploration methods used in reinforcement learning, is optimal from an information-theoretic point of view, in that it optimally trades expected return for the coding cost of the policy. Second, we address the problem of curiosity-driven learning. We propose that, in addition to maximizing the expected return, a learner should choose a policy that also maximizes the learner's predictive power. This makes the world both interesting and exploitable. Optimal policies then have the form of Boltzmann-style exploration with a bonus, containing a novel exploration-exploitation trade-off which emerges naturally from the proposed optimization principle. Importantly, this exploration-exploitation trade-off persists in the optimal deterministic policy, i.e., when there is no exploration due to randomness. As a result, exploration is understood as an emerging behavior that optimizes information gain, rather than being modeled as pure randomization of action choices.     

Coordinated activity of ventral tegmental neurons adapts to appetitive and aversive learning

Our understanding of how value-related information is encoded in the ventral tegmental area (VTA) is based mainly on the responses of individual putative dopamine neurons. In contrast to cortical areas, the nature of coordinated interactions between groups of VTA neurons during motivated behavior is largely unknown. These interactions can strongly affect information processing, highlighting the importance of investigating network level activity. We recorded the activity of multiple single units and local field potentials (LFP) in the VTA during a task in which rats learned to associate novel stimuli with different outcomes. We found that coordinated activity of VTA units with either putative dopamine or GABA waveforms was influenced differently by rewarding versus aversive outcomes. Specifically, after learning, stimuli paired with a rewarding outcome increased the correlation in activity levels between unit pairs whereas stimuli paired with an aversive outcome decreased the correlation. Paired single unit responses also became more redundant after learning. These response patterns flexibly tracked the reversal of contingencies, suggesting that learning is associated with changing correlations and enhanced functional connectivity between VTA neurons. Analysis of LFP recorded simultaneously with unit activity showed an increase in the power of theta oscillations when stimuli predicted reward but not an aversive outcome. With learning, a higher proportion of putative GABA units were phase locked to the theta oscillations than putative dopamine units. These patterns also adapted when task contingencies were changed. Taken together, these data demonstrate that VTA neurons organize flexibly as functional networks to support appetitive and aversive learning.     

Demonstration of experimental disinhibitory activity in a series of neuroleptic orthoanisamides

Among 3 orthoanisamides having different substitution of the nitrogen of a pyrrolidine ring, derivates ethyl (sulpiride) and propyl GRI 1665) show desinhibitory properties by the test of behavioural despair of Porsolt and coll, while the methyl derivative (TER 1546) is inactive.     

Classification of cortical neurons according to the character of their background impulse activity]

The method of basic components and cluster analysis was used to classify 75 units in the visual cortex of alert rabbits, proceeding from the empiric form of distribution of interspike intervals (DII), the mean frequency of impulsation and the relative number of intervals up to 500 msec. They were classified into nine groups containing from two to twelve units. Besides the cues, used as a basis for classification, the groups of units also differed in the structure of burst activity, the correlation of adjacent intervals and the ratio between the short (up to 20 to 60 msec) and long intervals. The latter served to make suggestions on the genetic affinity of bimodal DII to those with a bend on the waning after the maximum, and on the nature of formation of high frequency bursts and intervals exceeding 20 to 60 msec.     

Changes in cortical unit activity during selective reinforcement of a chosen interspike interval range

In experiments on immobilized unanesthetized rabbits selective automatic reinforcement of certain ranges of short and long interspike intervals in spontaneous unit activity recorded from single cortical units was given by means of a nociceptive stimulus. Analysis of postinterval histograms showed that the total number of intervals reinforceable by nociceptive stimuli is reduced as a result of the consequent reorganization of the firing pattern. If short intervals are reinforced the mean firing rate is reduced and the probability of appearance of long intervals immediately after the short reinforcements is increased. After reinforcement of long intervals the mean firing rate was increased in one group of cortical neurons, with a corresponding decrease in the total number of long intervals. In the other group of cells a decrease in the number of long intervals was accompanied by a decrease in the mean firing rate of the cells. It is postulated that reorganization of the firing pattern is determined by the level of synchronization of ascending activating influences and by their summation with phases of excitation and inhibition in reciprocally interacting neuron populations.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 339–348, July–August, 1972.     

Effect of temperature on impulse activity of cortical neurons in guinea pigs

The temperature change of incubating fluid from 37 to 24 degrees C results in significant decrease of neuronal spontaneous firing rate in parietal cortex slices. Evoked spike responses to microiontophoretic application of glutamate practically did not change.     

Kainic acid increases activity only of some cortical neurons in the rat

The influence of a subconvulsant dose of kainic acid (KA) on the activity of neurons was studied in the sensorimotor cortical area of urethane-anesthetized rats. A total of 41 neurons was recorded, 38 of these in layer V (probably pyramidal cells). The activity of 18 neurons was recorded before as well as more than 30 min after KA administration (6 mg/kg i.p.). Nine out of these 18 neurons increased their firing rate significantly even 20 min after KA injection, whereas the remaining neurons did not change their activity. Altogether, the increase in the firing rate was significant. KA was found to enhance markedly the firing rate of a part of cortical neurons at very early stages of its action.     

Reactivity of the cortical neurons to acetylcholine in rats

Activity of 55 neurons of the sensorimotor cerebral cortex of rats was recorded at iontophoretic application of acetylcholine. 36% of neurons exhibited an excitatory reaction, 30%--inhibitory-excitatory, 18%--inhibitory-excitatory-inhibitory and 16%--excitatory-inhibitory reactions; the type of reaction, in contrast to its expressiveness, did not depend on the the type of reaction, in contrast to its expressiveness, did not depend on the strength of phoresis current. Duration of the excitatory components entering reactions of all neurons formed a continuous series of values in the range of 1.4 to 16 s and had 2 maxima--at the 4-th and 8-th seconds. It is suggested that duration of this component of reaction reflects important functional properties of the nerve cell.     

Increased alpha2,3-sialylation and hyperglycosylation of N-glycans in embryonic rat cortical neurons during camptothecin-induced apoptosis

Alterations in the glycan chains of cell surface glycoconjugates are frequently involved biological processes such as cell-cell interaction, cell migration, differentiation and development. Cultured embryonic (E18) rat cortical neurons underwent apoptosis in response to camptothecin, and lectin histochemistry showed that binding to apoptotic neurons of FITC-conjugated Maackia amurensis agglutinin (MAA), which is specific for terminal alpha2,3-sialic acid residues, increased progressively with increasing concentrations of camptothecin. Analysis of the total proteins of apoptotic neurons by SDS-PAGE, and lectin blotting using HRP-labeled MAA, revealed that the expression of terminal alpha2,3-sialic acid residues on an unknown protein with an apparent molecular mass of 25.6 kDa also increased in apoptotic neurons. NP-HPLC analysis of the total cellular N-glycans of normal and apoptotic neurons demonstrated that the expression of structurally simpler biantennary types of N-glycans fell by 49% during apoptosis whereas the more branched triantennary types of N-glycans with terminal sialic acid residues increased by up to 59%. These results suggest that increased surface expression of alpha2,3-sialic acid residues and hyperglycosylation of N-glycans is a common feature of cellular responses to changes in cell physiology such as tumorigenesis and apoptosis.     

Trophic effect of beta-amyloid precursor protein on cerebral cortical neurons in culture

We investigated the effect of human beta-amyloid precursor protein (APP) on rat primary cerebral cortical neurons cultured in a serum-free medium. Two secretory APP species (APP667 and APP592) with and without the protease inhibitor domain were produced by COS-1 cells transfected with APP cDNAs, which encode the N-terminal portions of APP770 and APP695. Both highly purified APP species, when added to the medium, enhanced neuronal survival and neurite extension in a dose-dependent manner with a maximum effect at approximately 100 nM. These results suggest that secreted forms of APP have trophic activity for cerebral cortical neurons.     

Dynamics of cortical evoked activity during human learning to discriminate microintervals of time using feedback

The dynamics of the cortical evoked activity in the process of learning of time microintervals (10, 60 and 180 ms) discrimination was studied in healthy adults. Feedback stimulus visually informing of the real correlations of the differentiated pauses facilitates the discrimination. The factor of the visual field does not affect the estimation of brief time intervals. At correct identifications, the P300 wave is recorded with a higher amplitude, than at errors. In the trial following the "nonconfirming" feedback stimulus, the standard and test stimuli evoke in the left hemisphere a greater P300 wave, than in the trial after the "confirming" stimulus. Feedback influence is retained in the long-term memory.