Meeting Abstract
S1.1 Tuesday, Jan. 4 Coping with Variability in Small Neuronal Networks CALABRESE, Ronald L; Emory University ronald.calabrese@emory.edu
The small neuronal networks that comprise invertebrate CPGs display a 2-5 fold range of intrinsic membrane currents and synaptic strengths across animals and yet produce functional output. In the leech heartbeat CPG, the patterned output of premotor interneurons and the strength of their inhibitory synaptic outputs onto segmental motor neurons have been quantified. To understand how the pattern of premotor activity is produced, we created a model of all the identified interneurons of the CPG and their interconnections. We identified a few key inhibitory synaptic and electrical connections necessary to produce proper phase relations among the premotor interneurons and used a brute force approach to vary the strengths of these contacts and determine relative values that led to activity conforming to the range of activity observed among animals. The predicted connection strengths were then confirmed experimentally. To understand how motor neuron output is produced, we used an exemplar recording of spiking activity in all the intersegmental premotor interneurons as the temporal input and values averaged across animals for the inhibitory synaptic strengths from premotor interneurons to motor neurons in a model of motor neuron coordination. This model captured the gross intersegmental coordination but fell short of quantitative verisimilitude with phase data averaged across animals. We thus reassessed animal-to-animal variability in the pattern of synaptic strengths and in the temporal patterns of interneuronal input and of motor neuron output. All of these patterns, while on average true to the general conception of the fictive pattern, showed uncorrelated variability. Thus to arrive at a quantitatively accurate model of even a meticulously characterized neuronal network, it may be necessary to make all parameter and characteristic measurement in the same animal.
