Stimulation-Evoked Effective Connectivity (SEEC): An in-vivo approach for defining mesoscale corticocortical connectivity

BackgroundCortical electrical stimulation has been a versatile technique for examining the structure and function of cortical regions as well as for implementing novel therapies. While electrical stimulation has been used to examine the local spread of neural activity, it may also enable longitudinal examination of mesoscale interregional connectivity. Recent studies have used focal intracortical microstimulation (ICMS) with optical imaging to show cross-region spread of neural activity, but techniques are limited to utilizing hemodynamic responses within anesthetized preparations. ObjectiveHere, we sought to use ICMS in conjunction with recordings of multi-unit action potentials to assess the mesoscale effective connectivity within sensorimotor cortex. MethodsNeural recordings were made from multielectrode arrays placed into sensory, motor, and premotor regions during surgical experiments in three squirrel monkeys. During each recording, single-pulse ICMS was repeatably delivered to a single region. Mesoscale effective connectivity was calculated from ICMS-evoked changes in multi-unit firing. ResultsMulti-unit action potentials were able to be detected on the order of 1 ms after each ICMS pulse. Across sensorimotor regions, short-latency (< 2.5 ms) ICMS-evoked neural activity strongly correlated with known anatomic connections. Additionally, ICMS-evoked responses remained stable across the experimental period, despite small changes in electrode locations and anesthetic state. ConclusionsThese results show that monitoring ICMS-evoked neural activity, in a technique we refer to as Stimulation-Evoked Effective Connectivity (SEEC), is a viable way to longitudinally assess effective connectivity enabling studies comparing the time course of connectivity changes with the time course of changes in behavioral function. HighlightsO_LIShort-latency neural responses to ICMS were evaluated in multiple cortical regions. C_LIO_LINeural responses strongly correlated with known anatomical connections. C_LIO_LIStimulation-evoked neural responses were maintained across repeated tests. C_LIO_LIICMS-evoked activity can show longitudinal changes in effective connectivity. C_LI