An Electronic Circuit Model of the Interpostsynaptic Functional LINK Designed to Study the Formation of Internal Sensations in the Nervous System

Figure 8

Electronic circuit model for the interpostsynaptic functional LINK, which is shown in Figures 3 and 7. (a) Preliminary electronic circuit in the process of building the final circuit model of the interpostsynaptic functional LINK shown in (b). Simultaneous activation of two different neurons N_A and N_C (in green and violet, resp.) results in the formation of a functional LINK between the postsynaptic terminals at the synapses located at each one of their output terminals (presynaptic terminals). When neuron N_A is activated alone before associative learning, the output from the system occurs through , since both inputs of the logic gate AND6 receive current from the neuron N_A. Similarly, as long as neuron N_C is activated alone, output from the system occurs through , since both inputs of the logic gate AND7 receive current from neuron N_B. The interpostsynaptic functional LINK is represented by Latch1. When neurons N_A and N_C are activated simultaneously, Latch1 gets latched. Since the duration of the latch is not controlled, Latch1 remains latched and the logic gate AND2 will keep on receiving one of its inputs. Since many of the newly formed interpostsynaptic functional LINKs have half-lives, fine regulation of the duration of the interpostsynaptic functional LINKs is required to represent them and is shown in (b). After associative learning that involves simultaneous activation of neurons N_A and N_C in their pathways, activation of either one of the neurons N_A or N_C by either one of the stimuli that took part in associative learning is sufficient to provide the second input to AND2 through the logic gate OR1. When AND2 is activated, it activates the postsynaptic terminals of both synapses that are LINKed through the interpostsynaptic functional LINK. The activation of a postsynapse by activity entering from the lateral side in the absence of arrival of activity from its corresponding presynaptic terminal results in semblances, cellular hallucinations about possible features of the item whose memory is retrieved. Semblance formation is expected to occur in systems when (a) unidirectional activation occurs at the synapses, (b) continuous changes in potential of the postsynaptic terminal occur from quantal release of neurotransmitter from its presynaptic terminal, and (c) lateral entry of activity through the interpostsynaptic functional LINK contributes to the horizontal component of the oscillating neuronal activity; . (b) This circuit diagram is a modification of the circuit shown in (a). It has a voltage source S1 (in red) for providing pulses of miniature voltage changes due to quantal release from the presynaptic terminals that are represented in the circuit by the anodes of the diodes and . The additional features include controls for adjusting the duration of interpostsynaptic functional LINKs, the duration of outputs through the postsynaptic terminal dendrite, and the duration of reactivation of the functionally LINKed postsynaptic terminals, providing a flexible circuit to simulate the functioning of the nervous system. Once an interpostsynaptic functional LINK is formed, it remains in a dormant state for a certain period of time depending on its life-span. There are three latches, Latch1, Latch2, and Latch3. Latch1 represents the dormant interpostsynaptic functional LINK. If sensory inputs do not arrive through the neurons N_A or N_C, then the OR gate OR2 is closed. This activates the inverter IN1, which in turn activates three downstream timers Timer1, Timer2, and Timer3 that in turn control three downstream events. (1) The triggering of Timer1 controls the duration of functioning of Latch1, which represents the interpostsynaptic functional LINK. (2) The triggering of Timer2 controls the duration of functioning of Latch2 that determines the duration of activation of the postsynaptic terminals that are represented by the cathodes of diodes and (Diodes and represent synapses). (3) The triggering of Timer3 controls the duration of functioning of Latch3 that determines the duration of activity at postsynaptic dendrites and . Additional presynaptic terminals and , respectively, of neurons N_A and N_C are also shown; .

(a)  

(b)