Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Neural Network Populations of Neurons



Information theory provides the means for quantifying how much neurons communicate to other neurons, and thus provide a quantitative approach to fundamental questions about information processing in the brain. (Rolls & Deco; Noisy Brain, 57)

Across a population of cells, the firing rate information provided by each neuron tends to be independent; i.e. the information increases approximately linearly with the number of neurons. (Rolls & Deco; Noisy Brain, 61)

The number of stimuli that can be encoded rises exponentially as the number of neurons in the ensemble increases. (Rolls & Deco; Noisy Brain, 61)

There is little additional information, to the great deal available in the firing rates, from any stimulus-dependent cross-correlations of synchronization that may be present. (Rolls & Deco; Noisy Brain, 62)

There is little additional information to the great deal available in the firing rates, from the order on which spikes arrive from different neurons. (Rolls & Deco; Noisy Brain, 62)


Collective action of neural assemblies

Discharges associated with a single neuron often produce a rather consistent spike-like shape that differs significantly in its waveform from other nearby neurons. (Motter; Neurophysiology, 52)

Firing rate of a neuron is an ever-changing dynamic value that depends upon the momentary participation of the neuron in a neuronal assembly.

The variability in interspike intervals observed for many neurons in various locations in the nervous system is consistent with the presence of a random Poisson process. (Motter; Neurophysiology, 52)

Information appears to be coded within single neurons only by the average rate of firing and not by the precise composition of the intervals between spikes. (Motter; Neurophysiology, 52)

Cortical neurons receive around 5,000--10,000 synapses, of which about 85% are excitatory. If inputs arrived randomly, their integration would result in a fairly regular output train. (Motter; Neurophysiology, 53)

The effect of inhibition in cortical circuits is not simply an antagonistic balancing act versus excitation. Inhibition acts as a trimming damper on the explosive growth of positive feedback gain of excitatory cortical circuits. Relatively small amounts of inhibition provided at the correct time can shape the amplification of information. (Motter; Neurophysiology, 53)

Modeling studies emphasize the necessity of considering the collective action of neural assemblies in information processing. (Motter; Neurophysiology, 53)

Synaptic integration at most cortical synapses can be regulated by slow and long-acting neuromodulators. Many of these neuromodulator systems originate in areas of the basal forebrain and brainstem, areas that exert major state controls over waking and attentive behavior. (Motter; Neurophysiology, 53)

Population codes

Many variables in the brain are encoded with population codes. (Doya, et al.; Bayesian Brain, 115)

A major focus of theoretical neuroscience has been understanding how populations of neurons encode information about single variables and how this information can be decoded from the population activity. (Doya, et al.; Bayesian Brain, 115)

One of the few things in systems neuroscience we are fairly certain about is that information is encoded in population activity. (Doya, et al.; Bayesian Brain, 131)

Cortical neurons are unlikely to transmit information in the temporal pattern of spike discharge. Rather, we suggest that quantities are represented as rate codes in column-like ensembles of 50-100 neurons.


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