Skin Conductance as a Viable Alternative for Closing the Deep Brain Stimulation Loop in Neuropsychiatric Disorders

Abstract

Markers from local field potentials, neurochemicals, skin conductance, and hormone concentrations have been proposed as a means of closing the loop in Deep Brain Stimulation (DBS) therapy for treating neuropsychiatric and movement disorders. Developing a closed-loop DBS controller based on peripheral signals would require: (i) the recovery of a biomarker from the source neural stimuli underlying the peripheral signal variations; (ii) the estimation of an unobserved brain or central nervous system related state variable from the biomarker. The state variable is application-specific. It is emotion-related in the case of depression or post-traumatic stress disorder, and movement-related for Parkinson's or essential tremor. We present a method for closing the DBS loop in neuropsychiatric disorders based on the estimation of sympathetic arousal from skin conductance measurements. We deconvolve skin conductance via an optimization formulation utilizing sparse recovery and obtain neural impulses from sympathetic nerve fibers stimulating the sweat glands. We perform this deconvolution via a two-step coordinate descent procedure that recovers the sparse neural stimuli and estimates physiological system parameters simultaneously. We next relate an unobserved sympathetic arousal state to the probability that these neural impulses occur and use Bayesian filtering within an Expectation-Maximization framework for estimation. We evaluate our method on a publicly available data-set examining the effect of different types of stress on peripheral signal changes including body temperature, skin conductance and heart rate. A high degree of arousal is estimated during cognitive tasks, as are much lower levels during relaxation. The results demonstrate the ability to decode psychological arousal from neural activity underlying skin conductance signal variations. The complete pipeline from recovering neural stimuli to decoding an emotion-related brain state using skin conductance presents a promising methodology for the ultimate realization of a closed-loop DBS controller. Closed-loop DBS treatment would additionally help reduce unnecessary power consumption and improve therapeutic gains.

A mixed filter algorithm for sympathetic arousal tracking from skin conductance and heart rate measurements in Pavlovian fear conditioning

“…For instance, in behavioral learning experiments involving correct/incorrect responses, p 0 is the probability that a subject gets an answer correct at the very outset prior to any learning occurring (i.e., the chance probability) [51,52]. In our prior work on Bayesian filtering using skin conductance data, taking p 0 as the average probability of an SCR occurring in the whole experiment provided good results [42,45,82,83].…”

“…State-space methodologies to track internal brain dynamics could ultimately lead to the development of convenient wearable monitors for long-term patient care. PTSD, for instance, is often accompanied by symptoms of hyperarousal [44], and a wearable device for estimating arousal may be helpful in tracking the status of a patient over time [45].…”

A Marked Point Process Filtering Approach for Tracking Sympathetic Arousal From Skin Conductance

“…The rate at which SCRs occur, their amplitudes and the tonic level are three of the most common skin conductance-related measures of autonomic arousal used in the literature [41]. Our previous work in [42], [43] and [44] presented some of the first methods to estimate sympathetic arousal from skin conductance explicitly making use of the point process state-space approach. In our first approach described in [42], [43], we related an unobserved arousal state to the occurrence of neural impulses underlying SCR events.…”

“…Our previous work in [42], [43] and [44] presented some of the first methods to estimate sympathetic arousal from skin conductance explicitly making use of the point process state-space approach. In our first approach described in [42], [43], we related an unobserved arousal state to the occurrence of neural impulses underlying SCR events. We binned the impulses to form a sequence of 0's and 1's based on whether or not they occurred at a given time instance.…”

“…Note that each impulse has an amplitude (the height of each impulse captures the synchronized discharge effect from multiple neurons). In the figure, the underlying bursts of sudomotor nerve activity were extracted using our deconvolution approach in [43] ( [43] presents both a deconvolution strategy and an arousal state estimation method). Our state estimation approach in [42], [43]-which we label binary observation-based state estimation (BOBSE)-ignored the amplitudes of the neural stimuli when detecting arousal.…”