Theta oscillations in human cortex during a working-memory task: evidence for local generators.
Cortical theta appears important in sensory processing and memory. Intracanial electrode recordings provide a high spatial resolution method for studying such oscillations during cognitive tasks. Recent work revealed sites at which oscillations in the theta range (4-12 Hz) could be gated by a working-memory task: theta power was increased at task onset and continued until task offset. Using a large data set that has now been collected (10 participants/619 recording sites), we have sufficient sampling to determine how these gated sites are distributed in the cortex and how they are synchronized. A substantial fraction of sites in occipital/parietal (45/157) and temporal (23/280) cortices were gated by the task. Surprisingly, this aspect of working-memory function was virtually absent in frontal cortex (2/182). Coherence measures were used to analyze the synchronization of oscillations. We suspected that because of their coordinate regulation by the working-memory task, gated sites would have synchronized theta oscillations. We found that, whereas nearby gated sites (<20 mm) were often but not always coherent, distant gated sites were almost never coherent. Our results imply that there are local mechanisms for the generation of cortical theta.
Raghavachari
S
S
Department of Psychology, University of Pennsylvania, Philadelphia, PA 19104, USA.
Lisman
J E
JE
Tully
M
M
Madsen
J R
JR
Bromfield
E B
EB
Kahana
M J
MJ
D000293:Adolescent; D000328:Adult; D001683:Biological Clocks / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D013826:Theta Rhythm / Q000379:methods*