Effects of performance accuracy on intra-cycle alpha- and gamma-band cross frequency coupling between temporal lobe sites of behaving monkeys.
1. ARL NSMA;
2. Evelyn F. McKnight Brain Inst., Univ. Arizona, Tucson, AZ
Initial observations of the human alpha rhythm led to the hypothesis that alpha reflected a cortical idling rhythm (Jasper and Penfield, 1949; Pfurtscheller et al., 1996). Recent studies, however, have demonstrated a relationship between alpha rhythms and performance in working memory tasks (Jensen and Lisman, 2005; Klimesch et al., 1999). Other studies have indicated that cortical alpha and gamma activity show cross-frequency coupling during the execution of certain behaviors (von Stein et al., 2000; Palva and Palva, 2007). This interaction has been interpreted as the formation of "frequency assemblies", which theoretically could influence spike timing coordination, thereby altering ongoing computations (Varela et al., 1995; Jensen, 2007; Lisman, 2005; Robbe et al., 2006; Skaggs et al., 1996). In the present study, local field potential recordings were obtained from rhesus macaques with chronically implanted independently movable tetrodes. Several medial temporal lobe structures were examined to determine whether accuracy in a mnemonic task influenced alpha/gamma coupling in the same way observed by von Stein et al. (2000) in cat visual cortex. In order to assess cross frequency coupling, the original LFP signal was filtered in the respective bands, followed by a decomposition via Hilbert transform allowing for the extraction of phase and amplitude information. Subsequently, alpha phase and gamma amplitude were recombined to form a new signal, allowing for the determination of the effects of phase on amplitude. The results provide direct evidence for the existence of robust alpha and gamma rhythms in the primate temporal lobe. Surprisingly, some temporal areas (i.e., TE), but not others (e.g., perirhinal), distinguish between correct and incorrect performance as measured by the structure of the intra-cycle cross frequency coupling. These data suggest that frequency assemblies can form independently in separate brain regions, and that these assemblies can be sensitive to behavioral outcomes.
Grant/Other Support: AG003376; McKnight Brain Research Foundation
Keyword (Complete): oscillations; primate; frequency assembly; tetrode