Modeling alternation to synchrony with inhibitory coupling: A neuromorphicVLSI approach

We developed an analog very large-scale integrated system of two mutually i nhibitory silicon neurons that display several different stable oscillation s. For example, oscillations can be synchronous with weak inhibitory coupli ng and alternating with relatively strong inhibitory coupling. All oscillat ions observed experimentally were predicted by bifurcation analysis of a co rresponding mathematical model. The synchronous oscillations do not require special synaptic properties and are apparently robust enough to survive th e variability and constraints inherent in this physical system. In biological experiments with oscillatory neuronal networks, blockade of i nhibitory synaptic coupling can sometimes lead to synchronous oscillations. An example of this phenomenon is the transition from alternating to synchr onous bursting in the swimming central pattern generator of lamprey when sy naptic inhibition is blocked by strychnine. Our results suggest a simple ex planation for the observed oscillatory transitions in the lamprey central p attern generator network: that inhibitory connectivity alone is sufficient to produce the observed transition.