Cortical Networks and Conscious Awareness

Faces, Cortical Networks and Effective Connectivity

Alumit Ishai (Chair)
University of Zurich. Zurich, Switzerland

- Sunday, June 24. 2:30PM - 3:00 PM -

Face perception elicits activation within a distributed cortical network that includes visual (‘core’) regions, as well as limbic and prefrontal (‘extended’) regions, which process invariant and changeable facial features, respectively. Using fMRI and Dynamic Causal Modeling, we investigated effective connectivity and functional organization between and within the core and the extended systems. We found that the core system is hierarchically organized in a predominantly feed-forward fashion, and that the fusiform gyrus exerts the dominant influence on the extended system. Moreover, emotional faces increased the coupling between the fusiform gyrus and the amygdala, whereas famous faces increased the connectivity between the fusiform gyrus and the orbitofrontal cortex. Implications of these findings will be discussed in the context of conscious awareness, mental imagery, and face recognition deficits in prosopagnosic patients.

Fundamental antagonistic networks in the human cortex: implication to neuronal models of subjective awareness.

Rafi Malach
Weizmann Institute of Science. Rehovot, Israel

- Sunday, June 24. 3:00PM - 3:30 PM -

Could it be that activity in a small, isolated cortical network is sufficient for perceptual awareness? It may seem that besides being extremely counter-intuitive this conjecture can never be tested experimentally. Indeed how can we ever find out if some cortical network in our brain develops a subjective awareness of its own? Fortunately, there is at least one mental stat that may allow us to ‘peak’ into such an independent cortical activity. This mental state is paradoxically associated with moments of a particularly heightened perception, where we have the intuitive sense of ‘losing our selves’. I will review data, obtained from fMRI research, showing that during such intense moments, cortical regions associated with introspection are shut-off, leaving sensory cortex to be active on its own. Furthermore, this behavior reflects a more fundamental antagonistic relationship between ‘extrinsic’ networks engaged in perception, and more ‘intrinsically’ oriented cortical systems. While these experiments are far from proving that isolated network activity suffices for perceptual awareness- they provide a first step in this direction, and illustrate that such ‘minimal’ models of awareness are experimentally tractable.

Consciousness and effective connectivity in wakefulness and sleep

Giulio Tononi
University of Wisconsin. Madison, USA

- Sunday, June 24. 3:30PM - 3:30 PM -

According to a theoretical prediction (Tononi, 2004), consciousness depends critically not so much on firing rates, synchronization at specific frequency bands, or sensory input per se, but rather on the brain's ability to integrate information. This is contingent on the effective connectivity among functionally specialized regions of the thalamocortical system. In a series of experiments we used a combination of TMS and EEG to measure directly the changes in effective connectivity that occurs in the human brain when consciousness fluctuates across the sleep-wake cycle. We observed that, as vigilance drops, from light drowsiness to deep NREM sleep, the response of the brain to a direct cortical perturbation becomes larger and larger, while specific patterns of long-range activation are progressively impaired. During REM sleep, effective connectivity partially recovers. Further experiments suggested that the breakdown of effective connectivity observed during NREM sleep may be due to intrinsic bistability in thalamocortical networks between up- and down states.