Alterations of the temporal pattern of individual neurons impulse discharges, especially the transition from single spike activity (tonic firing) to grouped discharges (bursts), play an important role for neuronal information processing and synchronization in many physiological processes (sensory encoding, information binding, hormone release, sleep-wake cycles) as well as in disease (Parkinson, epilepsy). To examine the impact of the neuronal dynamics on the neurons sensitivity and synchronization we have used Hodgkin-Huxley-type model neurons with subthreshold oscillations. The individual neurons have been tuned from pacemaker-like tonic firing to bursting which typically goes through a broad range of chaotic dynamics.

With application of noise we have seen remarkable differences, depending 1) on the type of noise implementation (current vs. conductance noise, white noise vs. correlated noise) and 2) on the activity pattern (tonic, chaotic, bursting). Conductance noise as well as correlated noise have much stronger effects than the conventionally used current noise whereby the most significant changes appear when the neurons exhibit the most simple pattern, a pacemaker-like discharge. Corresponding phenomena have been observed in the synchronization studies which revealed mutual interdependencies between the alterations of the neurons coupling strength and neurons activity patterns. The neurons synchronise easiest when they are operating in the periodic bursting regime. This is not the case when the neurons exhibit chaotic discharges. However, the highest coupling strengths are required in the periodic tonic firing regime. This seemingly simple pattern is obviously governed by more complex dynamics than expected from a conventional pacemaker neuron. This may have significant functional implications for neuronal synchronization and sensitivity changes, for example, in thalamocortical circuits at the transitions from wake to sleep states as well as in patho-physiological situations, e.g for the development of epileptic seizures and Parkinsons tremor.

Supported by the EU Network of Excellence BioSim, Contract No. LSHB-CT-2004–005137