Neuronal activity in the brain gives rise to transmembrane currents that can be measured in the extracellular medium. Although the major contributor of the extracellular signal is the synaptic transmembrane current, other sources — including Na+ and Ca2+ spikes, ionic fluxes through voltage- and ligand-gated channels, and intrinsic membrane oscillations — can substantially shape the extracellular field. High-density recordings of field activity in animals and subdural grid recordings in humans, combined with recently developed data processing tools and computational modelling, can provide insight into the cooperative behaviour of neurons, their average synaptic input and their spiking output, and can increase our understanding of how these processes contribute to the extracellular signal.

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The origin of extracellular fields and currents — EEG, ECoG, LFP and spikes

Interneurons of the hippocampus

Theta Oscillations in the Hippocampus

Two-stage model of memory trace formation: a role for "noisy" brain states.

Neuronal gamma-band synchronization is found in many cortical areas, is induced by different stimuli or tasks, and is related to several cognitive capacities. Thus, it appears as if many different gamma-band synchronization phenomena subserve many different functions. I argue that gamma-band synchronization is a fundamental process that subserves an elemental operation of cortical computation. Cortical computation unfolds in the interplay between neuronal dynamics and structural neuronal connectivity. A core motif of neuronal connectivity is convergence, which brings about both selectivity and invariance of neuronal responses. However, those core functions can be achieved simultaneously only if converging neuronal inputs are functionally segmented and if only one segment is selected at a time. This segmentation and selection can be elegantly achieved if structural connectivity interacts with neuronal synchronization. I propose that this process is at least one of the fundamental functions of gamma-band synchronization, which then subserves numerous higher cognitive functions.

/pdf/neuronal-gamma-band-synchronization-as-a-fundamental-process-1eo9l9v02s.pdf

Neuronal gamma-band synchronization as a fundamental process in cortical computation.

Laminar distribution of hippocampal rhythmic slow activity (RSA) in the behaving rat: current-source density analysis, effects of urethane and atropine.

J. Czopf

Papers

Laminar distribution of hippocampal rhythmic slow activity (RSA) in the behaving rat: current-source density analysis, effects of urethane and atropine.

Restoration of rhythmic slow activity (θ) in the subcortically denervated hippocampus by fetal CNS transplants

Hippocampal evoked potentials and EEG changes during classical conditioning in the rat

Cellular activity of intracerebrally transplanted fetal hippocampus during behavior.

Hippocampal slow wave activity during appetitive and aversive conditioning in the cat.