|Title||Interlaminar feedback connections dominate in macaque inferotemporal cortex: in vivo and in silico studies|
|Publication Type||Conference Paper|
|Year of Publication||2011|
|Authors||Kerr, CC., Neymotin SA., Mo J., Schroeder CE., M D., & Lytton WW.|
|Conference Name||Society for Neuroscience|
Differences in the laminar organization of the alpha oscillation between primary sensory cortex and higher sensory areas are thought to be linked to differences in its functional significance. We hypothesized that attention would act via cortical feedback pathways to modulate activity in supragranular layers. The interlaminar projections in the neocortex would then act as extensions of the interareal feedback pathway to modulate activity in granular and infragranular layers. We used Granger causality to investigate the relative contributions of feedforward and feedback connections in a computer model of neocortex, confirming simulation results with physiological recordings. The simulation consisted of 4230 event-driven, rule-based neurons distributed among 6 cortical layers and 13 cell populations, driven by Poisson-distributed input. Attentional effects were modeled as increased input to supragranular layers. Experimentally, linear array multielectrodes were chronically implanted in the inferotemporal cortex of behaving macaques, allowing 14-channel local field potentials (LFPs) and multiunit activities to be recorded from each cortical layer. In the computer model, the strongest causal influences demonstrated were from supragranular to infragranular layers; causal involvement of the granular layer was more limited. Maximum causality from supragranular to infragranular layers occurred at frequencies in the alpha band. Experimental results showed maximum causality at 10 Hz without attention and 12 Hz with attention; overall causality was higher with attention. A similar shift was demonstrated in the model, with causality maxima at 8 Hz increasing to 11 Hz with attention. Attention in the simulation also increased alpha power, especially in supragranular layers (27% increase, compared to 10% in infragranular ones). Experimentally, attention was found to increase LFP alpha power in a similar pattern: supragranular power increased 19%, while infragranular power increased 13%. We found that a simple unpatterned input to supragranular layers resulted in causal patterns similar to those found with attention in vivo. This reconceptualization of the supra- to infragranular interlaminar projection as a continuation of the feedback interareal projection suggests that attentional modulation from higher cortical areas will produce activation of lower cortical layers phased at alpha peaks. It remains to be demonstrated how this feedback will affect the driving feedforward inputs conveying sensory information.