Inhibitory Mechanisms in Primary Somatosensory Cortex Mediate the Effects of Peripheral Electrical Stimulation on Tactile Spatial Discrimination

During and after 15-min occlusion of the middle cerebral artery (MCA) in cats, local CBF and neuronal activity were measured in cortical areas varying in the degree of CBF reduction. In an area within the ischemic center (primary auditory cortex, middle ectosylvian gyrus), CBF was severely suppressed. Click-induced auditory evoked potentials and evoked as well as spontaneous single-unit activity ceased within 1 min after occlusion. Recirculation resulted in a recovery of the different neurophysiological parameters with a time delay ranging from several minutes to 2 h. In two areas surrounding the ischemic focus (a visual area in the marginal gyrus and the forelimb representation area in the primary somatosensory cortex), CBF was reduced but remained above 30 ml/100 g/min during MCA occlusion. Visual flash-induced evoked potentials and somatosensory evoked potentials induced by median nerve electrical stimulation ceased in the corresponding areas with a somewhat slower time course as compared to the auditory responses and they recovered faster after recirculation. In another somatosensory area (hindlimb projection area in the primary somatosensory cortex), CBF stayed nearly at control levels during occlusion. Evoked potentials and single-unit activity induced by tibial nerve electrical stimulation decreased ∼5 min after occlusion and were abolished ∼5 min later. At that time, single-unit activity had changed to a nonresponsive pattern but persisted. However, potentials evoked transcallosally by electrical stimulation of the contralateral hemisphere were still recorded. After reopening the MCA, the recovery of neuronal functions was usually complete and occurred within ∼5 min. We conclude that attention has to be focused on those areas surrounding an acute ischemic focus that show either no or only slight CBF alterations. The functional impairment found in such areas is caused by the injury of subcortical structures leading to a cortical deafferentation. Considering the apparent lack of a CBF disturbance, such a condition should be distinguished from the so-called cortical ischemic penumbra.

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Cerebral blood flow regulation under activation of the primary somatosensory cortex during electrical stimulation of the forearm

Neurological Research ◽

10.1080/01616412.1999.11740980 ◽

1999 ◽

Vol 21 (6) ◽

pp. 579-584 ◽

Cited By ~ 7

Author(s):

Kazuyoshi Ichimi ◽

Hiroji Kuchiwaki ◽

Suguru Inao ◽

Mikine Shibayama ◽

Jun Yoshida

Keyword(s):

Blood Flow ◽

Cerebral Blood Flow ◽

Electrical Stimulation ◽

Somatosensory Cortex ◽

Flow Regulation ◽

Primary Somatosensory Cortex ◽

Blood Flow Regulation ◽

Stimulation Of

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Evoking highly focal percepts in the fingertips through targeted stimulation of sulcal regions of the brain for sensory restoration

10.1101/2020.11.06.20217372 ◽

2020 ◽

Author(s):

Santosh Chandrasekaran ◽

Stephan Bickel ◽

Jose L Herrero ◽

Joo-won Kim ◽

Noah Markowitz ◽

...

Keyword(s):

Electrical Stimulation ◽

Somatosensory Cortex ◽

Functional Imaging ◽

Intractable Epilepsy ◽

High Density ◽

Primary Somatosensory Cortex ◽

Sensory Impairment ◽

Viable Approach ◽

The Brain ◽

Stimulation Of

AbstractParalysis and neuropathy, affecting millions of people worldwide, can be accompanied by a significant loss of somatosensation. With tactile sensation being central to achieving dexterous movement, brain-computer interface (BCI) researchers have explored the use of intracortical electrical stimulation to restore sensation to the hand. However, current approaches have been restricted to stimulating the gyral areas of the brain while functional imaging suggests that the representation of fingertips lie predominantly in the sulcal regions. Here we show, for the first time, highly focal percepts can be evoked in the fingertips of the hand through electrical stimulation of the sulcal areas of the brain. To this end, we mapped and compared sensations elicited in the hand by stimulating both gyral and sulcal areas of the human primary somatosensory cortex (S1). Two participants with intractable epilepsy were implanted with stereoelectroencephalography (SEEG) and high-density electrocorticography (HD-ECoG) electrodes in S1 guided by high-resolution functional imaging. Using myelin content and cortical thickness maps developed by the Human Connectome Project, we elucidated the specific sub-regions of S1 where focal percepts were evoked. Within-participant comparisons showed that sulcal stimulation using SEEG electrodes evoked percepts that are significantly more focal, with 80% less area of spread (p=0.02) and localized to the fingertips more often than in gyral stimulation via HD-ECoG electrodes. Finally, sulcal locations exhibiting repeated modulation patterns of high-frequency neural activity during mechanical tactile stimulation of the hand showed the same somatotopic correspondence as sulcal stimulation. These findings show that minimally-invasive sulcal stimulation could lead to a clinically viable approach to restoring sensation in those living with sensory impairment.SignificanceIntracortical or cortical surface stimulation of the primary somatosensory cortex (S1) offers the promise of restoring somatotopically-relevant sensation in people with sensory impairment. However, evoking percepts in the fingertips has been challenging as their representation has been shown to be predominantly located within sulcal regions of S1 – inaccessible by these stimulation approaches. We evoked highly focal percepts in the fingertips of the hand by stimulating the sulcal regions of S1 in people with intractable epilepsy using stereoelectroencephalography (SEEG) depth electrodes. Sensory percepts in the fingertips were more focal and more frequently evoked by SEEG electrodes than by high-density electrocorticography (HD-ECoG) grids evidenced by within-participant comparisons. Our results suggest that fingertip representations are more readily targeted within the sulcal regions. SEEG electrodes potentially offer a clinically viable approach to access the sulcal regions for sensory neuroprostheses that can aid dexterous motor control.

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Homeostatic Metaplasticity in the Human Somatosensory Cortex

Journal of Cognitive Neuroscience ◽

10.1162/jocn.2008.20106 ◽

2008 ◽

Vol 20 (8) ◽

pp. 1517-1528 ◽

Cited By ~ 30

Author(s):

Barbara Bliem ◽

J. Florian M. Müller-Dahlhaus ◽

Hubert R. Dinse ◽

Ulf Ziemann

Keyword(s):

Electrical Stimulation ◽

Median Nerve ◽

Somatosensory Cortex ◽

Discrimination Threshold ◽

Spatial Discrimination ◽

High Frequency Stimulation ◽

Human Motor Cortex ◽

The Right ◽

Stimulation Of

Long-term potentiation (LTP) and long-term depression (LTD) are regulated by homeostatic control mechanisms to maintain synaptic strength in a physiological range. Although homeostatic metaplasticity has been demonstrated in the human motor cortex, little is known to which extent it operates in other cortical areas and how it links to behavior. Here we tested homeostatic interactions between two stimulation protocols—paired associative stimulation (PAS) followed by peripheral high-frequency stimulation (pHFS)—on excitability in the human somatosensory cortex and tactile spatial discrimination threshold. PAS employed repeated pairs of electrical stimulation of the right median nerve followed by focal transcranial magnetic stimulation of the left somatosensory cortex at an interstimulus interval of the individual N20 latency minus 15 msec or N20 minus 2.5 msec to induce LTD- or LTP-like plasticity, respectively [Wolters, A., Schmidt, A., Schramm, A., Zeller, D., Naumann, M., Kunesch, E., et al. Timing-dependent plasticity in human primary somatosensory cortex. Journal of Physiology, 565, 1039–1052, 2005]. pHFS always consisted of 20-Hz trains of electrical stimulation of the right median nerve. Excitability in the somatosensory cortex was assessed by median nerve somatosensory evoked cortical potential amplitudes. Tactile spatial discrimination was tested by the grating orientation task. PAS had no significant effect on excitability in the somatosensory cortex or on tactile discrimination. However, the direction of effects induced by subsequent pHFS varied with the preconditioning PAS protocol: After PASN20-15, excitability tended to increase and tactile spatial discrimination threshold decreased. After PASN20-2.5, excitability decreased and discrimination threshold tended to increase. These interactions demonstrate that homeostatic metaplasticity operates in the human somatosensory cortex, controlling both cortical excitability and somatosensory skill.

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