Primary Generators of Visually Evoked Field Potentials Recorded in the Macaque Auditory Cortex

Area of Science:

• Neuroscience
• Auditory Cortex Research
• Visual Processing

Background:

• Previous studies suggested local field potential (LFP) responses to faces in macaque auditory cortex, potentially indicating audiovisual integration.
• Field potentials (FPs) can reflect synaptic activity from both local and distant neuronal sites due to volume conduction.
• The assumption that FPs primarily represent local activity can be misleading if distant signals contaminate recordings.

Purpose of the Study:

• To investigate whether face-evoked responses recorded in the macaque auditory cortex are generated locally within this region.
• To differentiate between local neural activity and volume-conducted signals in auditory cortex recordings.
• To clarify the origin of face-evoked FPs previously reported in the auditory cortex.

Main Methods:

• Recorded field potentials (FPs) and multiunit activity using linear array multielectrodes across the auditory cortex in three macaques.
• Applied current source density (CSD) analysis to the laminar FP profile to identify local current generators.
• Examined underlying inferotemporal cortex for face-responsive activity and CSD profiles.

Main Results:

• CSD analysis revealed no significant local generator contribution to visual FPs within the auditory cortex.
• An increase in visual FP amplitude with cortical depth suggested generators located below the auditory cortex.
• The underlying inferotemporal cortex exhibited polarity inversions in main visual FP components, robust CSD responses, and high-amplitude multiunit activity.

Conclusions:

• Face-evoked FP responses in the macaque auditory cortex are not generated locally but are volume-conducted from the inferotemporal cortex.
• These findings underscore the critical need to account for far-field contamination in LFP recordings.
• The study cautions that LFP interpretations must consider potential superposition of distant neuronal activity, especially in layered cortical analyses.