Optical imaging of cortical networks via intracortical microstimulation

Abstract

Brock AA, Friedman RM, Fan RH, Roe AW. Optical imaging of cortical networks via intracortical microstimulation. J Neurophysiol 110: 2670 -2678. First published September 11, 2013 doi:10.1152/jn.00879.2012.-Understanding cortical organization is key to understanding brain function. Distinct neural networks underlie the functional organization of the cerebral cortex; however, little is known about how different nodes in the cortical network interact during perceptual processing and motor behavior. To study cortical network function we examined whether the optical imaging of intrinsic signals (OIS) reveals the functional patterns of activity evoked by electrical cortical microstimulation. We examined the effects of current amplitude, train duration, and depth of cortical stimulation on the hemodynamic response to electrical microstimulation (250-Hz train, 0.4-ms pulse duration) in anesthetized New World monkey somatosensory cortex. Electrical stimulation elicited a restricted cortical response that varied according to stimulation parameters and electrode depth. Higher currents of stimulation recruited more areas of cortex than smaller currents. The largest cortical responses were seen when stimulation was delivered around cortical layer 4. Distinct local patches of activation, highly suggestive of local projections, around the site of stimulation were observed at different depths of stimulation. Thus we find that specific electrical stimulation parameters can elicit activation of single cortical columns and their associated columnar networks, reminiscent of anatomically labeled networks. This novel functional tract tracing method will open new avenues for investigating relationships of local cortical organization. intrinsic signal optical imaging; electrical microstimulation PRIMATE CEREBRAL CORTEX is composed of a collection of cortical columns. These columns are 100-to 250-m-sized processing units that are interconnected to form distinct stimulusspecific processing networks. With this organization, the cerebral cortex is able to process information in parallel, perhaps best exemplified by the anatomical and functional organization found within visual cortical areas (see, e.g., Hubel 1984a, 1984b; Ts'o and Gilbert 1988). Anatomical and electrophysiological connectivity studies in V1 and V2 have revealed separate networks strongly associated with color processing (in the blobs in V1 and thin stripes in V2) and orientation selectivity (in the interblob regions and thick/pale stripes), respectively. Ongoing research is still revealing how these feature-specific networks generate the perception of the visual world.

Microelectrode array stimulation combined with intrinsic optical imaging: A novel tool for functional brain mapping

“…In an optical imaging study that examined the pattern of activation following focal electrical stimulation, local patchy activations were observed, similar in size and distribution to anatomically labeled patches following a focal tracer injection. These activation patterns were, moreover, relatively consistent following cortical stimulation at different laminar depths (15). In a 2-photon study that examined neuronal activation in response to electrical stimulation (typically less than 10 μA), the authors reported that the activated subpopulation (<300 μm zone) remained within the activation focus but that the subpopulation within the locus shifted, suggesting that the stimulated network was not randomly distributed.…”

“…Such methods have been developed in conjunction with intrinsic signal optical imaging (13-16), voltage sensitive dye imaging (17-19), and fMRI (20-22) following single site stimulation. These methods have revealed both local intra-areal and distant inter-areal connection patterns (15, 23). …”

Infrared neural stimulation: a new stimulation tool for central nervous system applications

“…Previous studies have demonstrated the use of focal electrical stimulation with optical imaging to map intra-areal or inter-areal connections. 27,28 However, the mapping of more global connections is better conducted with functional MRI (fMRI) methods, an approach that lacks the spatial resolution of intrinsic optical imaging but has the important advantage of being able to resolve changes in subsurface structures. Indeed, the potential for using light-based methods with fMRI for functional tract tracing has already been demonstrated.…”

Spatiotemporal Profile of Voltage-Sensitive Dye Responses in the Visual Cortex of Tree Shrews Evoked by Electric Microstimulation of the Dorsal Lateral Geniculate and Pulvinar Nuclei

“…In primates, the retinotopic organization of neurons is mirrored between each adjacent visual cortical area (Engel et al, 1994(Engel et al, , 1997DeYoe et al, 1996). In tree shrews, the retinotopic organization of area V1 has been characterized using intrinsic optical imaging techniques, but no maps could be obtained for extrastriate areas (Bosking et al, 2000(Bosking et al, , 2002. Unlike primates where the border between V1 and V2 occurs at the vertical meridian of the visual field, the transition between the two areas in tree shrew visual cortex takes place at 15°i n the ipsilateral visual field.…”

“…The accuracy of the stereotaxic dLGN location was confirmed by recording multiunit activity in response to contralateral and ipsilateral visual stimulation, because each of the six layers of the dLGN show preference for stimulus increments or decrements, ocular input, and retinotopic position (Conway and Schiller, 1983). Thus, electrodes were positioned in the dLGN to stimulate groups of neurons who's receptive-field locations matched the portion of V1 recorded by optical imaging (Bosking et al, 2000(Bosking et al, , 2002. Although, neurons in the dLGN have small, well defined receptive fields, pulvinar neuron receptive fields are diffuse and difficult to hand-map.…”