Ebner Marc Lateral Gap Junctions Consciousness Hameroff Germany

Jun 12, 2010 10:13 AM  ? working paper for Mardc Ebner and Stuart Hameroff

this is excellent work.  Marc is at Tubingen.Look at DISCUSSION on page 22

Marc addresses how their theory fits into all the other theories of CONSC.  Not Really.

see my remarks under discussion.

Cognitive brain functions, i.e. sensory perception, motor control and learning, are

understood as computation by axonal-dendritic chemical synapses in networks of integrate-

and-ﬁre neurons. Cognitive brain functions may occur either consciously, or non-consciously

(on ‘auto-pilot’). Conscious cognition is marked by gamma synchrony EEG, mediated

largely by dendritic-dendritic gap junctions, sideways connections in input/integration lay-

ers of neural networks. A theoretical model (the ‘conscious pilot’) suggests that, as gap junc-

tions open and close, a gamma-synchronized zone moves through the brain as an executive

agent, converting non-conscious ‘auto-pilot’ cognition to consciousness, and enhancing com-

putation by coherent processing and collective integration. In this study we implemented

sideways ‘gap junctions’ in a single layer artiﬁcial neural network to perceive and represent

a visual scene. The set of neurons connected through gap junctions form a reconﬁgurable

resistive grid or sub-network zone. In the model, out-going spikes are temporally integrated

and spatially averaged using the ﬁxed resistive grid set up by neurons of similar function

which are connected through gap junctions. This spatial average, essentially a feedback

signal from the neuron’s output, determines whether particular gap junctions between neu-

rons will open or close. Neurons connected through open gap junctions synchronize their

output spikes. The system demonstrates a moving zone of synchrony which correlates with

ﬁgure/ground separation, and models the neural correlate of consciousness (NCC) in the

brain.

Measurable brain activity correlating most closely with consciousness (i.e. the NCC)

is synchronized electrical activity in a particular frequency band (30 to 90 Hz) of the elec-

troencephalogram (EEG) called gamma synchrony (Gray & Singer, 1989; Ribary et al.,

1991). EEG signals including gamma synchrony are produced by membrane potentials

reﬂecting integration in dendrites and cell bodies, i.e. not from axonal ﬁrings. Gamma

synchrony can occur locally within a brain region, between neighboring regions, or globally

distributed among spatially separated brain regions.

The mechanism of long range gamma synchrony remains unclear. Melloni et al.

(2007) assume long range synchronization of neural assemblies to be the key event mediating

access to consciousness. Diﬀerent mechanisms which could induce synchronous oscillations

are reviewed by Ritz & Sejnowski (1997). Local gamma synchrony requires something

other than directional axonal-dendritic or axonal-cell body neurocomputation mediated

by chemical synapses and axonal ﬁrings. Local gamma synchrony depends on dendrites

of neighboring neurons fused and synchronized by electrical synapses, or gap junctions

(Dermietzel, 1998; Draguhn et al., 1998; Hormuzdi et al., 2004; Bennett & Zukin, 2004). In

the context of neural networks, gap junction electrical synapses form lateral, or sideways

connections mediating synchrony (‘sideways synchrony’) in input/integration layers.

As gap junctions open and close, neuronal groups linked laterally by gap junctions

Gap junctions are pores on membranes of adjacent cells composed of connexin pro-

teins which electrically synchronize and physically fuse the two cells, forming continuous

membranes and cell interiors. In the brain, gap junctions occur primarily between den-

drites of neighboring neurons and mediate gamma synchrony, the best measurable correlate

of consciousness. Gap junctions enable integration in dendrites of multiple neurons simul-

taneously, eﬀecting collective integration. In the context of artiﬁcial neural networks, gap

junctions are lateral, or sideways connections in input/integration layers.

page 22

DISCUSSION

Marc just shows the relation of his theory to the work of others.

He makes clear that this is just a LOCAL THEORY of interaction of adjacent neurons

by electric contact and does not solve or even address the global synchronization

that is required by global workspace theory or any of the other macro theories of consc.

The discussion is really unsatisfactory.

Ebner Marc Lateral Gap Junctions Consciousness Hameroff Germany

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