Spinal direct current stimulation modulates the activity of gracile nucleus and primary somatosensory cortex in anaesthetized rats

Abstract

Non-technical summary Stimulation of the human brain with direct current is a simple but effective neuromodulation technique that is becoming increasingly popular due to its potentiality for non-invasively treating a variety of neurological and neuropsychiatric disorders. Recently, this neuromodulation technique has been extended to the stimulation of the human spinal cord. Here we investigated the mechanisms of action of spinal direct current stimulation (sDCS) in anaesthetized rats. We found that sDCS can selectively modulate the spontaneous activity entering the brain through the spinal cord via the somatosensory system, consequently modulating both the internal state of the brain and its responsiveness to external somatosensory stimuli. These findings have at least two levels of significance: from a physiological perspective, they remark on the importance of the spinal cord in regulating the state of the brain; from a clinical perspective, they offer a mechanistic rationale for the development of sDCS as an effective bottom-up neuromodulation technique.Abstract Afferent somatosensory activity from the spinal cord has a profound impact on the activity of the brain. Here we investigated the effects of spinal stimulation using direct current, delivered at the thoracic level, on the spontaneous activity and on the somatosensory evoked potentials of the gracile nucleus, which is the main entry point for hindpaw somatosensory signals reaching the brain from the dorsal columns, and of the primary somatosensory cortex in anaesthetized rats. Anodal spinal direct current stimulation (sDCS) increased the spontaneous activity and decreased the amplitude of evoked responses in the gracile nucleus, whereas cathodal sDCS produced the opposite effects. At the level of the primary somatosensory cortex, the changes in spontaneous activity induced by sDCS were consistent with the effects observed in the gracile nucleus, but the changes in cortical evoked responses were more variable and state dependent. Therefore, sDCS can modulate in a polarity-specific manner the supraspinal activity of the somatosensory system, offering a versatile bottom-up neuromodulation technique that could potentially be useful in a number of clinical applications.

Does Trans-Spinal Direct Current Stimulation Alter Phrenic Motoneurons and Respiratory Neuromechanical Outputs in Humans? A Double-Blind, Sham-Controlled, Randomized, Crossover Study

“…Thus, during spontaneous ventilation, in which respiratory-related discharges of PMNs are primarily driven by bulbospinal inputs, early-I PMNs would be recruited before late-I PMNs according to the size principle of motoneuron recruitment established by Henneman et al (1965). Enhanced tidal volume after cathodal tsDCS is in line with previous reports demonstrating the potential of cathodal tsDCS stimulation to specifically facilitate spinal excitability (Alanis, 1953;Aguilar et al, 2011;Ahmed, 2011). It is also consistent with recent data obtained in both animals and humans showing the potential of cathodal polarization to specifically improve the recruitment of larger motor units (Ahmed and Wieraszko, 2012;Bocci et al, 2014).…”

Effects of Cathodal Trans-Spinal Direct Current Stimulation on Mouse Spinal Network and Complex Multijoint Movements

“…6 -8). Processing of movement initiation in the cortex (Isomura et al, 2009) could also be shortened during c-tsDC stimulation by potentiated tonic sensory feedback (Aguilar et al, 2011). Increasing amplitude and slope of movements indicate that c-tsDC stimulation reconfigures spinal circuitry to recruit larger motor units (Ahmed and Wieraszko, 2012).…”

“…When applied on the dorsum of the spinal cord, c-tsDC stimulation significantly enhances spinal excitability (Alanis, 1953;Eccles et al, 1962;Aguilar et al, 2011;Ahmed, 2011). This spinal facilitation can be exploited to restore motor or sensory function after brain or spinal cord injury.…”

“…Trans-spinal direct current (tsDC) stimulation is a neuromodulatory technique that causes immediate and long-term changes in spinal cord excitability (Aguilar et al, 2011;Ahmed, 2011Ahmed, , 2013Cogiamanian et al, 2011;Truini et al, 2011;Ahmed and Wieraszko, 2012;Cogiamanian et al, 2012;Lamy et al, 2012;Lamy and Boakye, 2013). The overarching goal of tsDC stimulation is to restore function that has been lost due to spinal cord or brain injuries.…”

Modulation of soleus H reflex by spinal DC stimulation in humans

“…In animals, few studies also investigated the effects of DC stimulation applied at the spinal cord level (transcutaneous spinal DC stimulation [tsDCS]) and have revealed the potential of tsDCS to become a powerful neurostimulation tool to modulate spinal cord excitability and corticospinal transmission (Aguilar et al 2011;Ahmed 2011;Eccles et al 1962;Fuortes 1954). Very recently, DC stimulation has also been applied to the human spinal cord.…”