Electrophysiological In Vitro Study of Long-Range Signal Transmission by Astrocytic Networks.

Astrocytes are diverse brain cells that form large networks communicating via gap junctions and chemical transmitters. Despite recent advances, the functions of astrocytic networks in information processing in the brain are not fully understood. In culture, brain slices, and in vivo, astrocytes, and neurons grow in tight association, making it challenging to establish whether signals that spread within astrocytic networks communicate with neuronal groups at distant sites, or whether astrocytes solely respond to their local environments. A multi-electrode array (MEA)-based device called AstroMEA is designed to separate neuronal and astrocytic networks, thus allowing to study the transfer of chemical and/or electrical signals transmitted via astrocytic networks capable of changing neuronal electrical behavior. AstroMEA demonstrates that cortical astrocytic networks can induce a significant upregulation in the firing frequency of neurons in response to a theta-burst charge-balanced biphasic current stimulation (5 pulses of 100 Hz × 10 with 200 ms intervals, 2 s total duration) of a separate neuronal-astrocytic group in the absence of direct neuronal contact. This result corroborates the view of astrocytic networks as a parallel mechanism of signal transmission in the brain that is separate from the neuronal connectome. Translationally, it highlights the importance of astrocytic network protection as a treatment target.

Correlations, feature-binding and population coding in primary visual cortex.

To test the hypothesis that correlated neuronal activity serves as the neuronal code for visual feature binding, we applied information theory techniques to multiunit activity recorded from pairs of V1 recording sites in anaesthetised cats while presenting either single or separate bar stimuli. We quantified the roles of firing rates of individual channels and of cross-correlations between recording sites in encoding of visual information. Between 89 and 96% of the information was carried by firing rates; correlations contributed 4-11% extra information. The distribution across the population of either correlation strength or correlation information did not co-vary systematically with changes in perception predicted by Gestalt psychology. These results suggest that firing rates, rather than correlations, are the main element of the population code for feature binding in primary visual cortex.