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Farhan A. Khawaja, James M. G. Tsui, Christopher C. Pack; Pattern motion selectivity of local field potentials in macaque visual cortex. Journal of Vision 2009;9(8):740. doi: 10.1167/9.8.740.
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© ARVO (1962-2015); The Authors (2016-present)
Local field potentials (LFPs) are low-frequency fluctuations in electrical activity that correspond to the total synaptic activity generated locally around the recording electrode. LFPs correlate well with EEG and fMRI BOLD signals and hold great promise for the design of brain-machine interfaces. However, it is unknown whether the LFP signal encodes the input from distant brain areas or the local processing within a circuit. Thus elucidating the source of the LFP signal is fundamental to our understanding of brain circuitry and for the interpretation of brain imaging studies.
We recorded single-units (SUs) and LFPs from a total of 229 sites from visual cortical areas V1, MT and MST of two awake, behaving macaque monkeys. We used grating and plaid stimuli to determine the motion direction selectivity of these areas. The number of pattern-selective SUs increased from V1 (6%) to MT (25%) to MST (60%) with only 9% of MST neurons being component-selective. Based on the scarcity of component selectivity in MST SU responses, we reasoned that a strongly component-selective LFP signal is likely to be a signature of visual feedforward input from lower cortical areas (e.g. V1, V2, V3 or MT). Consistent with this idea, we found robust component-selective LFP responses across all frequency bands, suggesting that feedforward input is responsible for a surprisingly large fraction of the LFP signal. Furthermore, the LFPs in MT were almost entirely component-selective, as is the feedforward input to this area from V1. Pattern-selective LFPs were found in the higher (gamma) frequency bands in MST, and they emerged in time before pattern-selective spiking activity. These results suggest a surprisingly strong link between the stimulus selectivity of cortical LFPs and that of the feedforward sensory input.
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