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Frequency-modulated (FM) sweeps are common components of vocalizations, including human speech. Both sweep direction and rate influence discrimination of vocalizations. Across species, relatively less is known about FM rate selectivity compared with direction selectivity. In this study, FM rate selectivity was studied in the auditory cortex of anesthetized 1- to 3-mo-old C57bl/6 mice. Neurons were classified as fast pass, band pass, slow pass, or all pass depending on their selectivity for rates between 0.08 and 20 kHz/ms. Multiunit recordings were used to map FM rate selectivity at depths between 250 and 450 μm across both primary auditory cortex (A1) and the anterior auditory field (AAF). In terms of functional organization of rate selectivity, three patterns were found. First, in both A1 and AAF, neurons clustered according to rate selectivity. Second, most (∼60%) AAF neurons were either fast-pass or band-pass selective. Most A1 neurons (∼72%) were slow-pass selective. This distribution supports the hypothesis that AAF is specialized for faster temporal processing than A1. Single-unit recordings (n = 223) from A1 and AAF show that the mouse auditory cortex is best poised to detect and discriminate a narrow range of sweep rates between 0.5 and 3 kHz/ms. Third, based on recordings obtained at different depths, neurons in the infragranular layers were less rate selective than neurons in the granular layers, suggesting FM processing undergoes changes within the cortical column. On average, there was very little direction selectivity in the mouse auditory cortex. There was also no correlation between characteristic frequency and direction selectivity. The narrow range of rate selectivity in the mouse cortex indicates that FM rate processing is a useful physiological marker for studying contributions of genetic and environmental factors in auditory system development, aging, and disease.

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Trujillo M, Razak KA. Altered cortical spectrotemporal processing with age-related hearing loss. J Neurophysiol 110: 2873-2886. First published September 25, 2013 doi:10.1152/jn.00423.2013.-Presbycusis (age-related hearing loss) is a prevalent disability associated with aging that impairs spectrotemporal processing, but the mechanisms of such changes remain unclear. The goal of this study was to quantify cortical responses to frequency-modulated (FM) sweeps in a mouse model of presbycusis. Previous studies showed that cortical neurons in young mice are selective for the rate of frequency change in FM sweeps. Here single-unit data on cortical selectivity and response variability to FM sweeps of either direction and different rates (0.08 -20 kHz/ms) were compared across young (1-3 mo), middle-aged (6 -8 mo), and old (14 -20 mo) groups. Three main findings are reported. First, there is a reduction in FM rate selectivity in the old group. Second, there is a slowing of the sweep rates at which neurons likely provide best detection and discrimination of sweep rates. Third, there is an increase in trial-to-trial variability in the magnitude and timing of spikes in response to sweeps. These changes were only observed in neurons that were selective for the fast or intermediate range of sweep rates and not in neurons that preferred slow sweeps or were nonselective. Increased variability of response magnitude, but not changes in temporal fidelity or selectivity, was seen even in the middle-aged group. The results show that spectrotemporal processing becomes slow and noisy with presbycusis in specific types of neurons, suggesting receptive field mechanisms that are altered. These data suggest neural correlates of presbycusis-related reduction in the ability of humans to process rapid spectrotemporal changes.

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Purpose: We describe two case studies that use embodiment in virtual reality as a treatment for chronic low back pain. The purpose of this case series was to determine the feasibility of a novel virtual reality-based digital therapeutic for the treatment of chronic pain. Patients and Methods: Two patients with chronic low back pain received seven sessions, two sessions per week, of a novel digital therapeutic that combines virtual embodiment with graded motor imagery to deliver functional rehabilitation exercises using an off-the-shelf virtual reality system. Pain intensity was measured using a visual analog scale before and after each session to get an indication whether individual sessions of virtual embodiment training decrease pain intensity. Pain catastrophizing scale was assessed before the first session and after the seventh session to determine the extent to which virtual embodiment training can improve psychological symptoms of chronic low back pain. Results: In both patients, pain intensity was improved after individual sessions of virtual embodiment training as measured by a paired t-test: (Patient A: t = 2.890, P < 0.05) and (Patient B: t = 5.346, P < 0.005). This indicates that individual sessions of virtual embodiment training decrease pain intensity. In both patients, improvements were observed in three subscales of the pain catastrophizing scale (rumination, magnification, and helplessness). This indicates that virtual embodiment training may have benefits for chronic pain symptoms such as pain intensity, pain-related mobility impairment, and disability. Conclusion: This case series provides evidence that embodiment in virtual reality improves symptoms of persistent chronic low back pain. We propose a mechanism by which virtual embodiment may improve chronic pain symptoms by recontextualizing sensory feedback from the body as patients engage in functional rehabilitation exercises while in virtual reality.

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While much attention is being given in the application of advanced technologies to improve upper extremity prostheses, traditional body-powered prostheses still remain the most popular by people with an amputation. A body-powered prosthesis provides the user with a reasonable solution for limb loss given their simple design, lower maintenance and initial cost. The two major types of body-powered prosthesis use either voluntary opening or voluntary closing control of the terminal device (or prehensor) used for holding and manipulating objects. What differentiates these two types of control is the relationship between the muscular force used to apply tension on the cable attached to the prehensor and the force produced by the prehensor. It has been argued that the voluntary closing prosthesis has more optimal compatibility between the muscle force and grip force of the prehensor. As a result, it may provide an advantage to the user in tasks requiring the control of grip force. To determine the effectiveness of the voluntary closing and voluntary opening prosthesis, we asked a person with a congenital quadruple limb deficiency who is right hand dominant, and that uses voluntary opening prostheses to participate in a study investigating grip force control. The participant was required to match different target grip forces displayed on a computer monitor by manipulating the pressure exerted on a hand dynamometer using either a voluntary closing or voluntary opening prosthesis. The participant only had previous experience with a voluntary opening prosthesis. The results showed that in several measures, the participant performed better with the voluntary closing prosthesis. These results provided support for the muscular force-grip force compatibility hypothesis.