The Bernstein Center Freiburg

Informal Seminar
Michael Denker

RIKEN Brain Science Institute, Wako City, Japan

Identifying assembly participation by combining local and mesoscopic measures of brain dynamics
Monday, January 11, 2010
11:00 h sharp
Lecture hall, ground floor
BCCN Building
Hansastr. 9a
A common hypothesis concerning the strategies of information coding employed by cortical networks involves the propagation of activity through synchronously firing groups of neurons, termed assemblies. Despite the inherent undersampling of brain dynamics, a growing body of experimental studies indirectly substantiates the assembly idea with findings of significant synchronous spiking activity that relates to behavior. Independently thereof, a signal measured directly at the population level, like the local field potential (LFP), typically exhibits temporally structured oscillations commonly interpreted as correlated network activity.

Recently, we demonstrated that the precision of spike-LFP locking is influenced by the LFP oscillation magnitude. Moreover, we established that Unitary Events (UEs, significant spike coincidences) exhibit an exceptionally strong locking to the LFP that cannot be explained by the locking of the individual neurons. Such UEs are a mixture of chance coincidences and excess coincidences stemming from the repeated, precise activation of an assembly. Here, we disentangle the two contributions based by integrating our previous results on LFP phase and amplitude.

In order to first understand how the observed levels of spike synchrony and phase locking quantitatively translate to the assembly hypothesis we formulate a conceptual model. It assumes that only part of the spiking activity is involved in assembly activations. In this framework, we demonstrate how to compute the relative contributions of assembly spikes following two conceptually different approaches. These percentages enable us to single out the spikes likely to originate from an assembly activation based on their LFP amplitude and locking characteristics. The consistency of our results encourages us that utilizing a mesoscopic mass signal subserves the detection of precise, transient synchronized spiking.
The talk is open to the public. Guests are cordially invited!