title: Organization of cortical and thalamic input to pyramidal neurons in mouse motor cortex.
abstract: Determining how long-range synaptic inputs engage pyramidal neurons in primary motor cortex (M1) is important for understanding circuit mechanisms involved in regulating movement. We used channelrhodopsin-2-assisted circuit mapping to characterize the long-range excitatory synaptic connections made by multiple cortical and thalamic areas onto pyramidal neurons in mouse vibrissal motor cortex (vM1). Each projection innervated vM1 pyramidal neurons with a unique laminar profile. Collectively, the profiles for different sources of input partially overlapped and spanned all cortical layers. Specifically, orbital cortex (OC) inputs primarily targeted neurons in L6. Secondary motor cortex (M2) inputs excited neurons mainly in L5B, including pyramidal tract neurons. In contrast, thalamocortical inputs from anterior motor-related thalamic regions, including VA/VL (ventral anterior thalamic nucleus/ventrolateral thalamic nucleus), targeted neurons in L2/3 through L5B, but avoided L6. Inputs from posterior sensory-related thalamic areas, including POm (posterior thalamic nuclear group), targeted neurons only in the upper layers (L2/3 and L5A), similar to inputs from somatosensory (barrel) cortex. Our results show that long-range excitatory inputs target vM1 pyramidal neurons in a layer-specific manner. Inputs from sensory-related cortical and thalamic areas preferentially target the upper-layer pyramidal neurons in vM1. In contrast, inputs from OC and M2, areas associated with volitional and cognitive aspects of movements, bypass local circuitry and have direct monosynaptic access to neurons projecting to brainstem and thalamus.
authors.affiliation: Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia 20147, USA. hooksm@janelia.hhmi.org
authors.forename: Bryan M
authors.initials: BM
authors.lastname: Hooks
authors.forename: Tianyi
authors.initials: T
authors.lastname: Mao
authors.forename: Diego A
authors.initials: DA
authors.lastname: Gutnisky
authors.forename: Naoki
authors.initials: N
authors.lastname: Yamawaki
authors.forename: Karel
authors.initials: K
authors.lastname: Svoboda
authors.forename: Gordon M G
authors.initials: GM
authors.lastname: Shepherd
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000166:cytology / Q000502:physiology*; D003627:Data Interpretation, Statistical; D004525:Efferent Pathways / Q000166:cytology / Q000502:physiology; D004558:Electric Stimulation; D055724:Electrophysiological Phenomena; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009044:Motor Cortex / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011149:Pons / Q000166:cytology / Q000502:physiology; D011712:Pyramidal Tracts / Q000166:cytology / Q000502:physiology*; D013788:Thalamus / Q000166:cytology / Q000502:physiology*