Laminar Profile and Physiology of the α Rhythm in Primary Visual, Auditory, and Somatosensory Regions of Neocortex.
The functional significance of the α rhythm is widely debated. It has been proposed that α reflects sensory inhibition and/or a temporal sampling or "parsing" mechanism. There is also continuing disagreement over the more fundamental questions of which cortical layers generate α rhythms and whether the generation of α is equivalent across sensory systems. To address these latter questions, we analyzed laminar profiles of local field potentials (LFPs) and concomitant multiunit activity (MUA) from macaque V1, S1, and A1 during both spontaneous activity and sensory stimulation. Current source density (CSD) analysis of laminar LFP profiles revealed α current generators in the supragranular, granular, and infragranular layers. MUA phase-locked to local current source/sink configurations confirmed that α rhythms index local neuronal excitability fluctuations. CSD-defined α generators were strongest in the supragranular layers, whereas LFP α power was greatest in the infragranular layers, consistent with some of the previous reports. The discrepancy between LFP and CSD findings appears to be attributable to contamination of the infragranular LFP signal by activity that is volume-conducted from the stronger supragranular α generators. The presence of α generators across cortical depth in V1, S1, and A1 suggests the involvement of α in feedforward as well as feedback processes and is consistent with the view that α rhythms, perhaps in addition to a role in sensory inhibition, may parse sensory input streams in a way that facilitates communication across cortical areas.


CONCLUSIONS
The α rhythm is thought to reflect sensory inhibition and/or a temporal parsing mechanism. Here, we address two outstanding issues: (1) whether α is a general mechanism across sensory systems and (2) which cortical layers generate α oscillations. Using intracranial recordings from macaque V1, S1, and A1, we show α band activity with a similar spectral and laminar profile in each of these sensory areas. Furthermore, α generators were present in each of the cortical layers, with a strong source in superficial layers. We argue that previous findings, locating α generators exclusively in the deeper layers, were biased because of use of less locally specific local field potential measurements. The laminar distribution of α band activity appears more complex than generally assumed.
Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York 10032, Cognitive Neuroscience and Schizophrenia Program, Nathan Kline Institute, Orangeburg, New York 10962, shaegens@gmail.com.
Saskia
http://orcid.org/0000-0002-9676-6275
S
Haegens
Cognitive Neuroscience and Schizophrenia Program, Nathan Kline Institute, Orangeburg, New York 10962, Department of Neuroscience and Physiology, New York University School of Medicine, New York, New York 10016.
Annamaria
A
Barczak
Department of Otolaryngology, Head and Neck Surgery, Stanford University, Stanford, California 94303, Center for Molecular and Behavioral Neuroscience, Rutgers University, Newark, New Jersey 07102.
Gabriella
G
Musacchia
Department of Radiology, Albert Einstein College of Medicine, Bronx, New York 10461, and.
Michael L
http://orcid.org/0000-0001-5421-8441
ML
Lipton
Department of Neurosurgery, Hofstra North Shore-LIJ School of Medicine and Feinstein Institute for Medical Research, Manhasset, New York 11030.
Ashesh D
AD
Mehta
Cognitive Neuroscience and Schizophrenia Program, Nathan Kline Institute, Orangeburg, New York 10962, Department of Neuroscience and Physiology, New York University School of Medicine, New York, New York 10016.
Peter
P
Lakatos
Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York 10032, Cognitive Neuroscience and Schizophrenia Program, Nathan Kline Institute, Orangeburg, New York 10962.
Charles E
CE
Schroeder
D000704:Analysis of Variance; D000818:Animals; D001931:Brain Mapping; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D008251:Macaca; D008297:Male; D019579:Neocortex / Q000033:anatomy & histology* / Q000502:physiology*; D009415:Nerve Net / Q000502:physiology*; D010507:Periodicity; D010812:Physical Stimulation; D013057:Spectrum Analysis
auditory; laminar; somatosensory; visual; α rhythm