Spatiotemporal pattern formation in neural systems.
Benjamin H. Singer · Deep Blue (University of Michigan) · 2007
Large scale coordination of neuronal activity in space and time has been observed throughout the brain. Spatiotemporal patterning has been implicated in sensory processing, where it is thought that oscillations play a physiologic role enabling functional correlation between groups of neurons coding stimulus features. At the same time, the propagation of inappropriately synchronous activity through neural networks is known to drive pathological brain function. We have pursued two sets of studies investigating the generation and progression of physiological and pathological spatiotemporal pattern formation in the brain. In the first set of studies, we have applied nonlinear time series analysis techniques to characterize network signaling during seizures in an in vitro model of epilepsy. By combining analysis of extracellular hippocampal recordings with a computational model, we suggest that seizures are divided into two phases. In the first phase, bursts are generated by intrinsic changes to a single location in the hippocampus. In the second phase, marked by multifocal activity, bursts result from propagation of residual activation among local networks. In the second set of studies, we examine the modulation of spatiotemporal patterning in the olfactory bulbs (OB) of the box turtle (Terrapina ornata). Using a computational model of olfactory bulb function, we suggest that oscillations in the olfactory bulb are modulated by centrifugal feedback from other cortical regions. The period-doubling transition which results may represent a shift from coding component-wise representation of odor inputs to whole-odor identity. Motivated by this computational result, we utilize paired-pulse stimulation to probe the influence of centrifugal connections on pattern formation in the OB in vivo. Paired-pulse stimulation of the OB results in a complex but reproducible increase in the spatial contrast of OB activity as measured by voltage sensitive dye imaging. Comparison of response modulation by serial ipsilateral and contralateral odorant stimulation suggests that odorant history exerts an effect in the OB via efferent connections from central odor processing regions. Both of these studies illustrate the importance of distributed network behavior and pattern formation for both physiologic and pathologic brain processes.