Large-Scale Organization of Rat Sensorimotor Cortex Based on a Motif of Large Activation Spreads

Abstract

Parcellation according to function (e.g., visual, somatosensory, auditory, motor) is considered a fundamental property of sensorimotor cortical organization, traditionally defined from cytoarchitectonics and mapping studies relying on peak evoked neuronal activity. In the adult rat, stimulation of single whiskers evokes peak activity at topographically appropriate locations within somatosensory cortex and provides an example of cortical functional specificity. Here, we show that single whisker stimulation also evokes symmetrical areas of suprathreshold and subthreshold neuronal activation that spread extensively away from peak activity, effectively ignoring cortical borders by spilling deeply into multiple cortical territories of different modalities (auditory, visual and motor), where they were blocked by localized neuronal activity blocker injections and thus ruled out as possibly caused by "volume conductance." These symmetrical activity spreads were supported by underlying border-crossing, long-range horizontal connections as confirmed with transection experiments and injections of anterograde neuronal tracer experiments. We found such large evoked activation spreads and their underlying connections regardless of whisker identity, cortical layer, or axis of recorded responses, thereby revealing a large scale nonspecific organization of sensorimotor cortex based on a motif of large symmetrical activation spreads. Because the large activation spreads and their underlying horizontal connections ignore anatomical borders between cortical modalities, sensorimotor cortex could therefore be viewed as a continuous entity rather than a collection of discrete, delineated unimodal regions, an organization that could coexist with established specificity of cortical organization and that could serve as a substrate for associative learning, direct multimodal integration and recovery of function after injury.

α4* Nicotinic Acetylcholine Receptors Modulate Experience-Based Cortical Depression in the Adult Mouse Somatosensory Cortex

“…1B,C; Table 1), and then progressively dissipated within 100 ms of stimulus onset. In agreement with multielectrode field recordings (Brett-Green et al, 2004;Frostig et al, 2008) and VSD imaging of whisker-evoked cortical responses (Ferezou et al, 2006, subsequent depolarizations were observed lateral to the barrel field in the secondary somatosensory (S2) cortex and then directly medial to the barrel-field in the PA cortex (Fig. 1D).…”

Spontaneous cortical activity alternates between motifs defined by regional axonal projections

“…However, VSD imaging can detect both sub-threshold and supra-threshold activity 18 . Given the relatively long time course of sub-threshold events, their contribution to VSD signals can be significant and may indicate a modulatory role 16,33 .…”

“…Unlike fMRI and intrinsic optical signal imaging 16,17 , VSD imaging measures electrical activity with relatively high spatial and temporal resolution 18 . VSD imaging has been applied across large regions of the mouse cortex to reveal fast, complex, localized and bilaterally synchronized patterns of depolarization 19 .…”

Voltage-Sensitive Dye Imaging Reveals Dynamic Spatiotemporal Properties of Cortical Activity after Spontaneous Muscle Twitches in the Newborn Rat

“…This also allowed us to examine the spatial and temporal properties of cortical sensory processing at young ages. In adult rodents, imaging tools have shown subthreshold activity to spread over large regions of the cortex after such stimulation (Wallace et al, 2004;Ferezou et al, 2007;Frostig et al, 2008;Desai et al, 2011;Mohajerani et al, 2011), but the extent to which this exists during development is not known. Images showing patterns of activity after limb and tail stimulation are shown in Figure 1B, and an example of the association between the VSD signal and EEG signal is shown in Figure 1C.…”

“…Whether such activity could contribute to the maturation of long-range connections present in the adult brain (Wallace et al, 2004;Ferezou et al, 2007;Frostig et al, 2008;Desai et al, 2011) is not known. The majority of research has examined its properties within a single sensory domain, either somatosensory (Milh, 2007;Marcano-Reik and Blumberg, 2008;Yang et al, 2009;Colonnese and Khazipov, 2010;Minlebaev et al, 2011) or visual Colonnese and Khazipov, 2010), and it is generally described as local and immobile (Yang et al, 2009).…”