Cesar Noronha
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Which sensations do we feel during intracortical microstimulations (ICMS)?
Which sensations do we feel during intracortical microstimulations (ICMS)?
Definition of ICMS: ICMS is the delivery of electrical current to the cortex across an implanted microelectrodes (VENKATRAMAN; CARMENA, 2011). The delivered current changes the quantity of eletrons inside the extracelular region, disturbing the intra-extracelular balance, what generates action potentials.
ICMS generating sensation: ICMS can be used to activate neuron populations on the somatosensory primary cortex (S1), the cortex that process sensation (VENKATRAMAN; CARMENA, 2011; VOIGT et al., 2017). This artificial activation of S1 is known to produces touch-like sensations. The human participants of ICMS experiments also report where they are feeling the artificial touch, what indicates ICMS also has proprioceptive properties (Cole and Cole, 1995). Based on this information, tha literature believes that ICMS is a solution for pacients with damage at the spinal cord. But the next step that ICMS needs to evolve is the quality of the sensation generated. Some subjects relates que sensation as "tingling" or "buzzing", what makes what is felt too artificial (Salas et al, 2018).
Salas et al. Methods: To resolve this problem Salea at al. proposed the study "Proprioceptive and cutaneous sensations in humans elicited by intracortical microstimulation". Where they use an human subject to investigate the sensations generated by different patterns of ICMS. For one section they vary the stimulated frequency and for other section they vary frequency and amplitude. The subject has 4 implanted arrays, where two are at S1 (check the image above).
Salas et al. Results: The image above shows the somatotopic map and the sensation modality found by Salas et al. after make the stimulation sections. On the left is the position on the arms and hands where the stimulation was felt. On the right we have the respective electrodes stimulated inside the array. the red and blue electrodes are respectively cutaneous and proprioception sensations. The gray cells means not was felt.
Another result found by Salas was a map of the sensation related with the amplitude and the frequency stimulated. For low amplitude and frequency there is no sensation. For the increase of frequency alone there is the beginning of the cutaneous sensation, while when we increase amplitude the is a increasing of proprioception sensation. Between 20 and 80 uA the feeling of both sensation increase with the amplitude, but just the proprioception increases 80 and 100 uA.
Noronha's discussion: These results indicate the relation between the felt sensation and the properties of the stimulated signal. The increase of amplitude and frequency generated a more sensations with in the ranged used. It indicates more current delivered were more able to activate the neurons of the stimulated regions for the ranged used.
Although increasing the current is an option to increase the quality of the stimulation, it also has nagative impactes at functional neuroprothesis. Salas et al observed each electrode alone, but in real reuroprothesis they will be stimulated together. Since all the electrodes are near each other, the stimulation may interfere bewtween them (BENALI et al., 2008).
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References:
Original Article Proprioceptive and cutaneous sensations in humans elicited by intracortical microstimulation
Michelle Armenta Salas, Luke Bashford, Spencer Kellis, Matiar Jafari, HyeongChan Jo, Daniel Kramer, Kathleen Shanfield, Kelsie Pejsa, Brian Lee, Charles Y Liu, Richard A Andersen
Abstract "Pioneering work with nonhuman primates and recent human studies established intracortical microstimulation (ICMS) in primary somatosensory cortex (S1) as a method of inducing discriminable artificial sensation. However, these artificial sensations do not yet provide the breadth of cutaneous and proprioceptive percepts available through natural stimulation. In a tetraplegic human with two microelectrode arrays implanted in S1, we report replicable elicitations of sensations in both the cutaneous and proprioceptive modalities localized to the contralateral arm, dependent on both amplitude and frequency of stimulation. Furthermore, we found a subset of electrodes that exhibited multimodal properties, and that proprioceptive percepts on these electrodes were associated with higher amplitudes, irrespective of the frequency. These novel results demonstrate the ability to provide naturalistic percepts through ICMS that can more closely mimic the body’s natural physiological capabilities. Furthermore, delivering both cutaneous and proprioceptive sensations through artificial somatosensory feedback could improve performance and embodiment in brain-machine interfaces."
BENALI, A.; WEILER, E.; BENALI, Y.; DINSE, H. R.; EYSEL, U. T. Excitation and inhibition jointly regulate cortical reorganization in adult rats. Journal of Neuroscience, Soc Neuroscience, v. 28, n. 47, p. 12284–12293, 2008.
VENKATRAMAN, S.; CARMENA, J. M. Active sensing of target location encoded by cortical microstimulation. IEEE Transactions on Neural Systems and Rehabilitation Engineering, IEEE, v. 19, n. 3, p. 317–324, 2011.
VOIGT, M. B.; HUBKA, P.; KRAL, A. Intracortical microstimulation differentially activates cortical layers based on stimulation depth. Brain stimulation, Elsevier, v. 10, n. 3, p. 684–694, 2017.
Cole J, Cole JO. 1995. Pride and a Daily Marathon. MIT Press.
