Intracortical Microstimulation (ICMS) activates motor cortex layer 5 pyramidal neurons mainly transsynaptically

Ahmed T. Hussin, Jeffery A. Boychuk, Andrew R. Brown, Quentin J. Pittman, G. Campbell Teskey

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

Background Intracortical microstimulation (ICMS) is a technique used for a number of purposes including the derivation of cortical movement representations (motor maps). Its application can activate the output layer 5 of motor cortex and can result in the elicitation of body movements depending upon the stimulus parameters used. Objective The extent to which pyramidal tract projection neurons of the motor cortex are activated transsynaptically or directly by ICMS remains an open question. Given this uncertainty in the mode of activation, we used a preparation that combined patch clamp whole-cell recordings from single layer 5 pyramidal neurons and extracellular ICMS in slices of motor cortex as well as a standard in vivo mapping technique to ask how ICMS activated motor cortex pyramidal neurons. Methods We measured changes in synaptic spike threshold and spiking rate to ICMS in vitro and movement threshold in vivo in the presence or absence of specific pharmacological blockers of glutamatergic (AMPA, NMDA and Kainate) receptors and GABAA receptors. Results: With major excitatory and inhibitory synaptic transmission blocked (with DNQX, APV and bicuculline methiodide), we observed a significant increase in the ICMS current intensity required to elicit a movement in vivo as well as to the first spike and an 85% reduction in spiking responses in vitro. Subsets of neurons were still responsive after the synaptic block, especially at higher current intensities, suggesting a modest direct activation. Conclusion Taken together our data indicate a mainly synaptic mode of activation to ICMS in layer 5 of rat motor cortex.

Original languageEnglish (US)
Pages (from-to)742-750
Number of pages9
JournalBrain Stimulation
Volume8
Issue number4
DOIs
StatePublished - 2015
Externally publishedYes

Keywords

  • Intracortical microstimulation
  • Motor cortex
  • Motor maps
  • Movement representations
  • Patch-clamping
  • Rat

ASJC Scopus subject areas

  • Biophysics
  • Neuroscience(all)
  • Clinical Neurology

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