Optical imaging of digit topography in individual awake and anesthetized squirrel monkeys

Abstract

Topographic maps and columnar structures are fundamental to cortical sensory information processing. Most of the knowledge about detailed topographic maps and columnar structure comes mainly from experiments conducted on anesthetized animals. Towards the goal of evaluating whether topographic maps change with respect to behavioral demands, we used intrinsic signal optical imaging in alert monkeys to examine the spatial specificity of cortical topographic representation. Specifically, the somatotopies of neighboring distal finger pad representation in areas 3b and 1 were examined in the same awake and anesthetized squirrel monkey. In comparison to the anesthetized animal, we found larger cortical activation sizes in the alert animal in area 3b, where activation widths were found to overlap with even non-adjacent digits. This may suggest that in the alert animal, there is less inhibition across the somatotopic map within area 3b.

Intra- and inter-subject variability of high field fMRI digit maps in somatosensory area 3b of new world monkeys

“…These patches are ~1 mm in diameter, and are well differentiated from each other and from their surroundings (Nelson et al, 1980; Sur et al, 1981; Sur et al, 1982; Pons et al, 1987). Secondly, during stimulation of single distal fingerpads in anesthetized squirrel monkeys, OIS mapping of area 3b at ~50 μm spatial resolution also reveals focal, distinct, millimeter sized activations with limited overlap (~10 %) between adjacent digits (Chen et al, 2001; Chen et al, 2003, , 2009). Finally, the homologous area in human SI with comparable somatotopic organization has also been identified with BOLD fMRI (Nelson and Chen, 2008; Schweizer et al, 2008).…”

Cell‐poor septa separate representations of digits in the ventroposterior nucleus of the thalamus in monkeys and prosimian galagos

“…The topographic representations of the glabrous hand in dorsolateral area 3b of somatosensory cortex of squirrel monkeys and galagos have been well established by microelectrode mapping methods (Carlson and Welt, 1980; Sur et al, 1980, 1982; Wu and Kaas, 2003) and more recently by optical imaging (Chen et al, 2005, 2009) in squirrel monkeys. As in other monkeys, digits 1–5 are represented in a lateral to medial sequence in rostral area 3b, and the pads of the palm are represented adjacently in caudal area 3b.…”

Cortical topography of intracortical inhibition influences the speed of decision making

“…Therefore, the response options between fingers are mapped onto distance in cortical coordinates. This relationship is based on the topographic mapping of the body surface onto cortical space, which in the case of finger representations displays a remarkable order (9,10,30,31). A second crucial prerequisite comes from the observation that interaction within the cortical map is spatially structured, consistent with the Mexican-hat component used in our model (10,51).…”

“…This relationship is based on the topographic mapping of the body surface onto cortical space, which in the case of finger representations displays a remarkable order (9,10,30,31). A second crucial prerequisite comes from the observation that interaction within the cortical map is spatially structured, consistent with the Mexican-hat component used in our model (10,51). By using distance-dependent cortical interaction, we explicitly connect behavioral space to corresponding cortical map dimensions, which enables our model to account for distance-specific effects of RT data, thereby extending the potential functional role of cortical maps.…”

“…On the other hand, experimental studies have focused on the extent and size of topographic maps, thereby exploring how and where physical stimuli and their attributes are localized and represented in the brain. Cortical lateral interaction seems to play a crucial role in the integration of information from remote skin portions, which is required for localization and discrimination (9)(10)(11), contour integration, as well as contextual influences by surrounding elements (12,13). Accordingly, cortical processing is modulated by nonlinear interactions through range-dependent intracortical excitation and inhibition.…”