Ipsilateral Stimulus Encoding in Primary and Secondary Somatosensory Cortex of Awake Mice

• Type of Material: Article
• Authors: Aurélie Pala, Georgia Institute of Technology; Garrett Stanley, Emory University
• Language: English
• Date: 2022-03-30
• Publisher: SOC NEUROSCIENCE
• Publication Version: Final Published Version
• Copyright Statement: © 2022 the authors
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1523/JNEUROSCI.1417-21.2022
• Title of Journal or Parent Work: JOURNAL OF NEUROSCIENCE
• Volume: 42
• Issue: 13
• Start Page: 2701
• End Page: 2715
• Grant/Funding Information: This work was supported by Swiss National Science Foundation Postdoctoral Fellowships P2ELP3_168506 and P300PA_177861 to A.P., National Institute of Neurological Disorders and Stroke BRAIN Grant R01NS104928 to G.B.S., and National Institute of Neurological Disorders and Stroke Grant R21NS112783 to A.P. and G.B.S.
• Keywords: somatosensation; Neurosciences; PARIETAL CORTEX; RAT BARREL CORTEX; Neurosciences & Neurology; WHISKER VIBRATION; CORPUS-CALLOSUM; CORTICAL LAYERS; secondary somatosensory cortex; RECEPTIVE-FIELDS; CEREBRAL-CORTEX; Science & Technology; CORTICOCORTICAL CONNECTIONS; stimulus coding; ipsilateral; SOMATOTOPIC ORGANIZATION; AREA SII; Life Sciences & Biomedicine; awake mouse
• Research Categories: Engineering, Biomedical

Abstract

Lateralization is a hallmark of somatosensory processing in the mammalian brain. However, in addition to their contralateral representation, unilateral tactile stimuli also modulate neuronal activity in somatosensory cortices of the ipsilateral hemisphere. The cellular organization and functional role of these ipsilateral stimulus responses in awake somatosensory cortices, especially regarding stimulus coding, are unknown. Here, we targeted silicon probe recordings to the vibrissa region of primary (S1) and secondary (S2) somatosensory cortex of awake head-fixed mice of either sex while delivering ipsilateral and contralateral whisker stimuli. Ipsilateral stimuli drove larger and more reliable responses in S2 than in S1, and activated a larger fraction of stimulus-responsive neurons. Ipsilateral stimulus-responsive neurons were rare in layer 4 of S1, but were located in equal proportion across all layers in S2. Linear classifier analyses further revealed that decoding of the ipsilateral stimulus was more accurate in S2 than S1, whereas S1 decoded contralateral stimuli most accurately. These results reveal substantial encoding of ipsilateral stimuli in S1 and especially S2, consistent with the hypothesis that higher cortical areas may integrate tactile inputs across larger portions of space, spanning both sides of the body.SIGNIFICANCE STATEMENT Tactile information obtained by one side of the body is represented in the activity of neurons of the opposite brain hemisphere. However, unilateral tactile stimulation also modulates neuronal activity in the other, or ipsilateral, brain hemisphere. This ipsilateral activity may play an important role in the representation and processing of tactile information, in particular when the sense of touch involves both sides of the body. Our work in the whisker system of awake mice reveals that neocortical ipsilateral activity, in particular that of deep layer excitatory neurons of secondary somatosensory cortex (S2), contains information about the presence and the velocity of unilateral tactile stimuli, which supports a key role for S2 in integrating tactile information across both body sides.