Local and remote functional connectivity of neocortex under the inhibition influence

Abstract: The current paper focuses on a relatively new and promising area of the study of EEG transformations during brain information processing based on the reduction of the signal to the discrete quasi-stationary segment sequences which may reflect individual brain microstates or discrete operations. In this framework, the complex brain functions require integration of several operations throughout the whole neocortex. However, the role of inhibitory brain systems in such processes is still unsettled. The effects of a single dose (30µg/kg) of lorazepam on the operational activity of neuronal populations and on the temporal binding between them were examined in a double-blind randomized crossover placebo-controlled study with 8 healthy volunteers. EEG measures at 20 channels were evaluated on two occasions: (1) eyes closed, (2) eyes open. In short, we conducted a two-by-two factorial study where one factor manipulated GABAergic neurotransmission (lorazepam versus placebo), while the other factor was simply brain state (eyes closed versus eyes opened). We were primarily interested in the main effect of lorazepam. In the present study, a connection between the mesoscopic level, described by the local functional processes (neuronal assemblies or populations) and the macroscopic level, described as a sequence of metastable brain states (remote functionally synchronized neuronal populations) was established. The role of inhibitory brain systems facilitated by lorazepam in the operational dynamics of neuronal populations and in the process of EEG structural synchrony (topological peculiarities) was addressed for the first time. It was shown that GABA signalling reorganized the dynamics of local neuronal populations and the remote functional connectivity between them. Keywords: Binding problem; Neuronal populations; Neural Assemblies; Synchronization; Operational/structural synchrony; EEG; Brain operations; GABA; Lorazepam; Inhibition

NeuroImage. 2004, V. 22. No 3. P. 1390-1406.

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