Correlated neuronal activity and the flow of neural information

Abstract

For years we have known that cortical neurons collectively have synchronous or oscillatory patterns of activity, the frequencies and temporal dynamics of which are associated with distinct behavioural states. Although the function of these oscillations has remained obscure, recent experimental and theoretical results indicate that correlated fluctuations might be important for cortical processes, such as attention, that control the flow of information in the brain.Research in systems neuroscience has traditionally focused on how neurons represent the world and on the mechanisms that endow neurons with their response properties or receptive fields. However, an equally important, but less well understood, aspect of brain function is how neurons communicate. For instance, the presence of a red light in the visual field might be irrelevant if in a theatre, but crucial if about to cross a road. The neural representation of the red light might be, at some level, the same in the two situations, but this information is then redirected and prioritized in totally different ways. Little is known about how, depending on the current behavioural requirements, neural signals are routed or assessed in the nervous system. There is evidence that timing is crucial: a recent study 1 showed that whether intracortical microstimulation influences performance in a sensory discrimination task depends on the time at which the microinjected current is delivered relative to the natural stimulus onset. This indicates that even a simple discrimination paradigm is executed according to an internal schedule, such that the information provided by the sensory neurons is effectively transmitted only during a certain time window. So, the temporal dynamics of neuronal interactions seem to be important for the gating processes that control the information that goes through at a given time.On the other hand, networks of neurons show highly complex temporal dynamics. It is well known from electroencephalographic studies 2 that the small voltage signals recorded from the scalp fluctuate at various frequencies, with dominant frequency components shifting according to behaviour. Slow oscillations with a strong 0.75-4-Hz component are associated with certain stages of sleep, whereas oscillations dominated by the 14-40-Hz band are typical of active, awake states 3,4 . Direct measurement of field potentials from the cortex reveals even higherfrequency components in the 40-200-Hz range 5 . At the single-neuron level, collective oscillations in cortical neurons have been documented for several years [6][7][8] . One functional interpretation is that this rhythmic behaviour is, again, related to higher-order sensory representations, but this idea continues to be hotly debated 9,10 . The problem is not that oscillations are not there, but that linking them to behaviour has been difficult.

Regulation of spike timing in visual cortical circuits

“…The experiments and models that we have summarized here indicate that inhibitory interneurons have a more dynamic role, one that might be of critical importance for regulating the flow of information in the cortex by controlling spike timing and synchrony in cortical circuits 132 .…”

Does schizophrenia arise from oxidative dysregulation of parvalbumin-interneurons in the developing cortex?

“…PV-interneurons are involved in the generation of gamma oscillations, which regulate working memory and information transmission between cortical areas (Salinas and Sejnowski, 2001;Bartos et al, 2007). In particular, synaptic inhibition from PVinterneurons controls the firing rates of pyramidal neurons, synchronizes spikes within populations of neurons, and participates in the development of executive functions associated with prefrontal brain regions (Kawaguchi and Kubota, 1993;Goldman-Rakic, 1999;Markram et al, 2004).…”

EEG gamma-band synchronization in visual coding from childhood to old age: Evidence from evoked power and inter-trial phase locking

“…Gamma-band synchronization has been linked to several cognitive functions in a range of studies (see Engel et al, 1992Herrmann et al, 2004;Singer and Gray, 1995;Tallon-Baudry, 2003;Tallon-Baudry and Bertrand, 1999 for reviews). Furthermore, it has been shown that the precise timing of pre-and post-synaptic activation determines long-term changes in synaptic strength (Bi and Poo, 1998;Markram et al, 1997) and that synchronization of synaptic inputs in the gamma band directly enhances their effective synaptic strength (König et al, 1996;Salinas and Sejnowski, 2001). Regardless of the exact roles of gamma oscillations in cognitive functioning (cf.…”