| Abstract: | Coherent oscillations in the theta-to-gamma frequency range have been proposed as a mechanism that coordinates neural activity in large-scale cortical networks in sensory, motor, and cognitive tasks. Whether this mechanism also involves coherent oscillations at delta frequencies (1–4 Hz) is not known. Rather, delta oscillations have been associated with slow-wave sleep. Here, we show coherent oscillations in the delta frequency band between parietal and frontal cortices during the decision-making component of a somatosensory discrimination task. Importantly, the magnitude of this delta-band coherence is modulated by the different decision alternatives. Furthermore, during control conditions not requiring decision making, delta-band coherences are typically much reduced. Our work indicates an important role for synchronous activity in the delta frequency band when large-scale, distant cortical networks coordinate their neural activity during decision making.Studies of the neural correlates of decision making in behaving monkeys have mainly been based on the analysis of firing rate patterns of neurons in individual cortical circuits, recorded one by one in succession, while trained monkeys perform sensory, motor, and cognitive tasks (1–3). These studies showed that the neuronal activities distributed across parietal and frontal lobe cortices correlate with processes that lead to decision making (4–7). However, how these spatially distant, cortical circuits coordinate their activities into a unified functional network during decision making remains poorly understood.It has been proposed that coherent oscillations of neuronal activities constitute a putative dynamical mechanism for mediating the interaction between different subsets of brain areas (8–11). Simultaneous recording from multiple intracortical areas in monkeys showed that the coherent higher frequency (beta and gamma bands) oscillations are linked to a broad variety of cognitive functions (12–18). Cortical oscillations at lower frequencies (theta and alpha bands) have also been discussed in terms of long-range integrative processes (19, 20). In fact, recent evidence showed theta-band coupling between visual area V4 and prefrontal cortex during short-term memory (21) and among the rat prefrontal cortex, ventral tegmental area, and hippocampus during working memory (22). It remains, however, probing whether coherent delta-band oscillations play a functional role in the interaction between cortical circuits. Delta-band oscillations are typically associated with slow-wave sleep (SWS; ref. 23), but an important question is whether delta-band oscillations during SWS and waking states represent the same underlying phenomenon (24). Recent findings associated delta-band oscillations in individual cortical areas with attention (25). In monkey primary visual cortex (26) and human motor cortex (27), delta-band oscillations entrain to the rhythm of external sensory events in an attention-dependent manner.Here, we examined whether coherent oscillations coordinate the activity of five simultaneously recorded cortical areas in the monkey performing a somatosensory discrimination task (7). We specifically focused on whether coherent delta-band oscillations play a significant functional role in linking cortical circuits during decision making. |
