Abstract
Cross-frequency coupling (CFC) between slow and fast brain rhythms, in the form of phase–amplitude coupling (PAC), is proposed to enable the coordination of neural oscillatory activity required for cognitive processing. PAC has been identified in the neocortex and mesial temporal regions, varying according to the cognitive task being performed and also at rest. PAC has also been observed in the anterior thalamic nucleus (ATN) during memory processing. The thalamus is active during the resting state and has been proposed to be involved in switching between task-free cognitive states such as rest, in which attention is internally-focused, and externally-focused cognitive states, in which an individual engages with environmental stimuli. It is unknown whether PAC is an ongoing phenomenon during the resting state in the ATN, which is modulated during different cognitive states, or whether it only arises during the performance of specific tasks. We analyzed electrophysiological recordings of ATN activity during rest from seven patients who received thalamic electrodes implanted for treatment of pharmacoresistant focal epilepsy. PAC was identified between theta (4–6 Hz) phase and high frequency band (80–150 Hz) amplitude during rest in all seven patients, which diminished during engagement in tasks involving an external focus of attention. The findings are consistent with the proposal that theta–gamma coupling in the ATN is an ongoing phenomenon, which is modulated by task performance.
Highlights
Neuronal activity oscillates at multiple frequency ranges, transiently forming synchronous networks associated with cognitive processing (Llinas, 1988; Hutcheon and Yarom, 2000; Varela et al, 2001; Buzsáki and Draguhn, 2004)
We show that theta–HFB phase–amplitude coupling (PAC) is present in the anterior thalamic nucleus (ATN) during the resting state, with HFB activity peaking at varying phases in the theta cycle across participants
PAC between theta (4–6 Hz) oscillations and HFB (80–150 Hz) activity was greater during rest than during tasks with an external focus of attention and involved a broader HFB frequency range
Summary
Neuronal activity oscillates at multiple frequency ranges, transiently forming synchronous networks associated with cognitive processing (Llinas, 1988; Hutcheon and Yarom, 2000; Varela et al, 2001; Buzsáki and Draguhn, 2004). Low frequency oscillations (LFOs), which includes those in the theta range, are modulated by the external environment via sensory and motor inputs and by endogenous cognitive processes (Schroeder and Lakatos, 2009; Canolty and Knight, 2010). Slower rhythms enable long-range communication between remote brain areas, with their phase reflecting local neuronal excitability (Canolty and Knight, 2010), while high frequency activity (high frequency band; HFB, 60–200 Hz) is believed to underlie information processing in localized cortical regions (Canolty et al, 2006; Jensen et al, 2007). To further examine the role of thalamic PAC in cognitive processing, we investigated whether thalamic PAC is a continuous phenomenon, modulated by external events, or whether it arises only at specific points in time to support goal-related cognitive processes
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