A model of the neural mechanisms responsible for pattern recognition and stimulus specific habituation in toads

Abstract

A neural model of the mechanisms possibly responsible for stimulus-specific habituation in toads is proposed. The model follows the hypothesis that prey-predator recognition is performed by command units as a result of retina-tectum-pretectum interaction. The model allow us to study the possible coding that the nervous system of toads uses for different prey stimuli, the neural mechanisms of habituation and dishabituation, and the dynamic changes that the command units may have during these processes. The model proposes specific hypothesis and experiments to clarify the nature of these processes and to test the validity of the command unit hypothesis.

A Neural Model of Synaptic Plasticity Underlying Short-term and Long-term Habituation

“…As mentioned earlier, short-term habituation involves alterations in neurotransmitter release, whereas long-term habituation seems to involve structural changes such as the number of presynaptic terminals (varicosities) and the number and size of active zones (Bailey & Chen, 1988a, 1988b. It is interesting to note that similar mechanisms also underlie short-term and long-term synaptic plasticity at the frog neuromuscular junction (Magleby & Zengel, 1982;Herrera, Grinnell & Wolowske, 1985 Stanley, 1976;Lara & Arbib, 1985;Gluck & Thompson, 1987;Ogmen & Moussa, 1993). The distinction between these two kinds of modeling resembles that between the detailed Hodgkin-Huxley equations (Hodgkin & Huxley, 1952) for a single neuron's action potential generation and the more abstract models of FitzHugh (1961) and Nagumo, Arimoto, and Yoshizawa (1962) (Wang & Arbib, 1991a), which helped to design a set of experiments to test and actually validate some of the predictions (Wang & Ewert, 1992 Although the learning gate model of Ciaccia, Maio, and Vacca (1992) addresses conditioning while ours models habituation, some comparisons may be drawn about how STM relates to LTM in these two models.…”

The Release of Visual Behavior in Toads: Stages of Parallel/Hierarchical Information Processing

“…These are presumably associated with a "negative value" by telencephalic "habituating neurons" and translated into a build-up of inhibition on tectal T5.2 neurons which is mediated via thalamic relay neurons. Computer simulations with model networks suggest that in the course of such a hypothesized process, information related to an "image" of stimulus cues is stored in prosencephalic structures that can be compared with the present stimulus (Lara & Arbib 1985; see also Lara, this volume). 2DG studies and lesion experiments show that the telencephalic posteroventral medial pallium (vMP), for example, plays an important role in long-term habituation which can be regarded as non-associative learning (see Finkenstadt, this volume).…”

Simulation of habituation to simple and multiple stimuli

“…These models compute various stimuli but place the emphasis on the study of conditioning, and do not cover reproduction of the basic properties of habituation, such as variations according to ISI or dishabituation. On the other hand, the model of Lara (1983) considers habituation to two stimuli, but deals with the matter from the perspective of neuronal networks with different physiological layers, an approach that differs from those of the models mentioned above as references for the one we shall present. Moreover, Lara's model does not function in real time, and nor, therefore, does it adjust to the stimulus-related changes that occur as a result of previous events; it requires a priori definition of the values of diverse initial variables, such as interval between stimuli and between different series of them, number of times each stimulus is presented, its intensity, and other parameters.…”