Simulation of a Neuronal Network operating Rhythmically through Recurrent Inhibition

Abstract

A SYNCHRONOUS afferent volley initiates a series of rhythmic discharges in the ventrolateral nucleus in the thalamus¹, due to repetitive activity in a recurrent inhibitory pathway of the thalamic neurones². A similar pattern of rhythmic activity occurs spontaneously in animals anæsthetized with barbiturates. An inhibitory phasing theory has been offered as an explanation for the spontaneous rhythm³. According to this theory, a period of rhythmic activity, usually lasting 1–2 sec, is triggered off by the discharge of one cell, which, through a recurrent inhibitory pathway utilizing one or several interneurones, is producing inhibitory postsynaptie potentials in a number of neighbouring cells. When the inhibitory potentials subside, the neurones will be in a state of post-anodal exaltation, often leading to depolarization of the cell with discharges. Similar depolarizing potentials have been seen in response to hyperpolarizing pulses^4–6 or inhibitory postsynaptic potentials^7,8 in many types of neurones. In the thalamus, the post-inhibitory firing will initiate another cycle, engaging an increased number of cells, and so on, until a large proportion of the neurones in a group beat in unison. At this point, a cell, discharging prematurely, may recruit other neurones to discharge at its own rhythm, and thereby start the disruption of the dominant rhythm.