Collaboration of trained and foreign neurons during formations of a local instrumental reflex.

At present it is not clear how instrumental actions arise. In our experiments the mollusk Helix received an aversive stimulus when one of its neurons did not generate an action potential in response to a conditioned stimulus. The appearance of an aversive stimulus did not depend on the generation or failure of a spike in the control neuron. Although the trained and the control neurons were not coupled and did not connect directly by synapses, the magnitudes of the conditioned responses of both the trained and the control neurons depended on the relationship between the nearest previous neuronal responses and the rapidity of their change. These relationships changed several times during learning, and depended on the initial excitability of the control neurons. The trial-and-error method may have revealed itself at the neuronal level.

Instrumental conditioning of the activity of putative command neurons in the mollusk Helix.

Gaining insight into the mechanism of generation of goal-directed actions is understanding neural function. In this study we examined the role of the action potential (AP) in a single molluscan neuron (responsible for a defensive response) in an instrumental behavior. The intracellular electrical activity of two neurons was recorded simultaneously. One neuron was trained and the other served as a control neuron. When the trained neuron produced an AP in response to a conditioned stimulus (CS), the mollusc did not receive a painful stimulus. Delivery of the painful stimulus did not depend on the response of the control neuron. The number of AP's in a trained neuron, the AP latency and the threshold revealed a bell-shaped dependence on learning, whereas the response of the control neuron to a CS decreased during learning. It is apparently feasible to elaborate this type of instrumental reflex, so that the discharge of a single neuron may serve as an instrumental action for the entire animal. The membrane potential in a trained neuron varies significantly during instrumental learning, but the change do not correspond to the dynamics of the instrumental reaction in the response to a CS. The control neuron exhibited weak but significant hyperpolarization during learning. The onset of the EPSP is determined by the timing of AP generation in presynaptic neurons. However, it changed in the trained neuron the elaboration of a instrumental reflex. The alterations in the latency of EPSP's during learning were significant, but were not consistent with the time history of the conditioned response. Therefore, although the learning procedure was directed to only one neuron, the presynaptic neurons and neurons at the same neuronal level (command-like neurons of the same behavior) participated in the learning. The sign of the participation was not necessarily the same as that in the trained neuron.

A mathematical model of neural information processing at the cellular level.

The basis for this neuronal model is that the properties of excitable membranes are controlled by biochemical reactions occurring in the nerve cells. The kinetics of these supposed chemical reactions is described by a set of first order differential equations. We considered the effect of regulation of the properties of sodium channels. This allows the simulation of the changes in the neuron's electrical activity parameters occurring during learning, associated with its excitability. The neuronal model exhibits different excitability after the learning procedure relative to the different input signals that corresponds to the experimental data.

Selective form of an excitable membrane plasticity.

This work describes the change in an active electrogenesis of the command neurons responsible for defensive closure of a snail's pneumostome during elaborating, extinction and restoration of a classical conditioned defensive reflex to a tactile stimulus. Tactile stimulations applied to different parts of a snail's body served as a differential stimulus. As the biological value of a conditioned stimulus increases due to learning, the excitability of command neurons in response to conditioned stimulus rises. At the same time the neurons demonstrated a reduced excitability in response to a differentiating stimulus.