Neuromodulation : journal of the International Neuromodulation Society
-
Neuropathic pain affects various dimensions of patient health including physical, psychological, and socioeconomic. The spectrum of psychological dysfunction that accompanies this pain phenotype is unknown, as well as differences based on the etiology of the pain among patients referred for spinal cord stimulation (SCS). ⋯ The high frequency of depressive and anxiety symptoms screened by the Beck scores in this cohort is an order of magnitude higher than seen in the general population. That many of these cases are undiagnosed should motivate clinicians from primary care providers, comprehensive pain specialists, and surgeons to screen SCS patients for such psychopathology. This represents an opportunity to enhance overall pain management as well as success with invasive neuromodulation strategies.
-
Spinal cord stimulation (SCS) treats neuropathic pain through retrograde stimulation of dorsal column axons and their inhibitory effects on wide dynamic range (WDR) neurons. Typical SCS uses frequencies from 50-100 Hz. Newer stimulation paradigms use high-frequency stimulation (HFS) up to 10 kHz and produce pain relief but without paresthesia. Our hypothesis is that HFS preferentially blocks larger diameter axons (12-15 µm) based on dynamics of ion channel gates and the electric potential gradient seen along the axon, resulting in inhibition of WDR cells without paresthesia. ⋯ At clinical HFS frequencies and pulse widths, HFS preferentially blocks larger-diameter fibers and concomitantly recruits medium and smaller fibers. These effects are a result of interaction between ion gate dynamics and the "activating function" (AF) deriving from current distribution over the axon. The larger fibers that cause paresthesia in low-frequency simulation are blocked, while medium and smaller fibers are recruited, leading to paresthesia-free neuropathic pain relief by inhibiting WDR cells.
-
A definition of free will is the ability to select for or against a course of action to fulfill a desire, without extrinsic or intrinsic constraints that compel the choice. Free will has been linked to the evolutionary development of flexible decision making. In order to develop flexibility in thoughts and behavioral responses, learning mechanisms have evolved as a modification of reflexive behavioral strategies. The ultimate goal of the brain is to reduce uncertainty inherently present in a changing environment. A way to reduce the uncertainty, which is encoded by the rostral anterior cingulate, is to make multiple predictions about the environment which are updated in parallel by sensory inputs. The prediction/behavioral strategy that fits the sensory input best is then selected, becomes the next percept/behavioral strategy, and is stored as a basis for future predictions. Acceptance of predictions (positive feedback) is mediated via the accumbens, and switching to other predictions by the dorsal anterior cingulate cortex (ACC) (negative feedback). Maintenance of a prediction is encoded by the pregenual ACC. Different cingulate territories are involved in rejection, acceptance and maintenance of predictions. Free will is known to be decreased in multiple psychopathologies, including obsessive compulsive disorder and addictions. ⋯ Successful neuromodulation increases the capacity to choose from different options for the affected individual, as well as inhibiting unwanted options, therefore increasing free will and free won't.