The Role of the Tectal Column in Facilitation of Amphibian Prey-catching

We used computer analysis of differential equations to study the properties of a family of models of a unit of neural circuitry in the amphibian tectum, the tectal column. Computer experiments were used to discriminate among various hypotheses and to suggest new experiments. Particular attention was paid to physiological data on facilitation of amphibian prey-catching behavior which led us to model the facilitation in terms of dynamic activity in the tectal column rather than in terms of synaptic modification. In the present paper, we propose a mathematical model of the amphibian tectal column to account for the facilitatory effects of prey-catching activity when prey stimuli are presented. The model is based on anatomical and physiological studies of this region and behavioral results observed in facilitation of prey-catching activity. The structure of the tectum shares many properties with other brain regions, which allow us to supplement the available tectal data. The model proposed is flexible and offers several alternatives that could be tested experimentally to constrain the number of possible mechanisms proposed. The current model uses simple differential equations to represent the time course of the membrane voltage of the cell and uses threshold functions to compute the corresponding action potentials. The model was simulated on a Digital Equipment Corp. VAX 11/780. Our work is informed by the following features that brain regions share in their sensorimotor processing of information: (1) In many systems, afferents are processed initially by a synaptic complex, a glomerulus comprising specific connections between axonal and dendritic terminals which may be interconnected, enclosed in glial membranes, or otherwise set apart. This synaptic complex has been described in many brain regions (Shepherd, 1970, 1974; Szentagothai, 1970; Szekely and Lazar, 1976), such ’ The research reported in this paper was supported in part by National Institutes of Health Grant NS14971. We thank David Ingle and Peter Ewert for valuable discussions of the experimental data and Donald House for his help with the computer graphics. ’ Present address: Universidad National Autonoma de Mexico, Centro de Investigaciones en Fisiologia Celular, A.P. 70-600, Mexico 20,