Abstract
Cortical gamma activity (30–80 Hz) is believed to play important functions in neural computation and arises from the interplay of parvalbumin-expressing interneurons (PV) and pyramidal cells (PYRs). However, the subthreshold dynamics underlying its emergence in the cortex of awake animals remain unclear. Here, we characterized the intracellular dynamics of PVs and PYRs during spontaneous and visually evoked gamma activity in layers 2/3 of V1 of awake mice using targeted patch-clamp recordings and synchronous local field potentials (LFPs). Strong gamma activity patterned in short bouts (one to three cycles), occurred when PVs and PYRs were depolarizing and entrained their membrane potential dynamics regardless of the presence of visual stimulation. PV firing phase locked unconditionally to gamma activity. However, PYRs only phase locked to visually evoked gamma bouts. Taken together, our results indicate that gamma activity corresponds to short pulses of correlated background synaptic activity synchronizing the output of cortical neurons depending on external sensory drive.
Highlights
Cortical activity in the gamma range (30–80 Hz) has been the focus of considerable attention in the last two decades
The neocortex is the main substrate of cognitive activity of the mammalian brain. It exhibits an oscillatory activity in the gamma range (30–80Hz), which is believed to play an important functional role and is altered in schizophrenic patients
Experimental studies have shown that gamma activity arises from the interaction of excitatory pyramidal neurons, the main neuronal type of the cortex, and local inhibitory neurons expressing the protein parvalbumin (PV)
Summary
Cortical activity in the gamma range (30–80 Hz) has been the focus of considerable attention in the last two decades. Gamma phase locking of extracellularly recorded units is most prominent in layers 2/3 [10], increases with selective attention [8], and correlates with shortened reaction times as well as maximized signal to noise ratios [11,12]. This synchronization is believed to improve local processing and to facilitate the transfer of information to higher-order cortical areas [4,7,13,14,15,16,17,18]. Recent studies using optogenetics in rodents have brought support to this hypothesis, showing that gamma activity improves tactile detection [19] and depends on the activity of parvalbumin-expressing fast-spiking interneurons (PV) [20,21]
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