Information theoretic evidence for layer- and frequency-specific changes in cortical information processing under anesthesia

Nature relies on highly distributed computation for the processing of
information in nervous systems across the entire animal kingdom. Such
distributed computation can be more easily understood if decomposed into
the three elementary components of information processing, i.e., storage,
transfer and modification, and rigorous information theoretic measures for
these components exist. However, the distributed computation is often also
linked to neural dynamics exhibiting distinct rhythms. Thus, it would be
beneficial to associate the above components of information processing
with distinct rhythmic processes where possible. Here we focus on the
storage of information in neural dynamics and introduce a novel
spectrally-resolved measure of active information storage (AIS). Drawing
on intracortical recordings of neural activity in ferrets under anesthesia
before and after loss of consciousness (LOC), we show that
anesthesia-related modulation of AIS is highly specific to different
frequency bands and that these frequency-specific effects differ across
cortical layers and brain regions. We found that in the high/low gamma
band, the effects of anesthesia result in AIS modulation only in the
supergranular layers, while in the alpha/beta band, the strongest decrease
in AIS can be seen at infragranular layers. Finally, we show that the
increase of spectral power at multiple frequencies, in particular at alpha
and delta bands in frontal areas, that is often observed during LOC
('anteriorization') also impacts local information processing –
but in a frequency-specific way: Increases in isoflurane concentration
induced a decrease in AIS in the alpha frequencies, while they increased
AIS in the delta frequency range $<2$Hz. Thus, the analysis of
spectrally-resolved AIS provides valuable additional insights into changes
in cortical information processing under anaesthesia.