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Cortical Electrocorticogram (ECoG) Is a Local Signal

Dubey, Agrita and Ray, Supratim (2019) Cortical Electrocorticogram (ECoG) Is a Local Signal. In: JOURNAL OF NEUROSCIENCE, 39 (22). pp. 4299-4311.

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Official URL: https://doi.org/10.1523/JNEUROSCI.2917-18.2019


Electrocorticogram (ECoG), obtained by low-pass filtering the brain signal recorded from a macroelectrode placed on the cortex, is extensively used to find the seizure focus in drug-resistant epilepsy and is of growing importance in cognitive and brain-machine-interfacing studies. To accurately estimate the epileptogenic cortex or to make inferences about cognitive processes, it is important to determine the ``spatial spread'' of ECoG (i.e., the extent of cortical tissue that contributes to its activity). However, the ECoG spread is currently unknown; even the spread of local field potential (LFP) obtained from microelectrodes is debated, with estimates ranging from a few hundred micrometers to several millimeters. Spatial spread can be estimated by measuring the receptive field (RF) and multiplying by the cortical magnification factor, but this method overestimates the spread because RF size gets inflated due to several factors. This issue can be partially addressed using a model that compares the RFs of two measures, such as LFP and multi-unit activity (MUA). To use this approach for ECoG, we designed a customized array containing both microelectrodes and ECoG electrodes to simultaneously map MUA, LFP, and ECoG RFs from the primary visual cortex of awake monkeys (three female Macaca radiata). The spatial spread of ECoG was surprisingly local (diameter similar to 3 mm), only 3 times that of the LFP. Similar results were obtained using a model to simulate ECoG as a sum of LFPs of varying electrode sizes. Our results further validate the use of ECoG in clinical and basic cognitive research.

Item Type: Journal Article
Additional Information: copyright for this article belongs to SOC NEUROSCIENCE
Keywords: electrocorticogram; local field potential; magnification factor; primary visual cortex; receptive field; spatial spread
Department/Centre: Division of Biological Sciences > Centre for Neuroscience
Date Deposited: 24 Jun 2019 18:28
Last Modified: 24 Jun 2019 18:28
URI: http://eprints.iisc.ac.in/id/eprint/63050

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