Shannon and Renyi Entropies to Classify Effects of Mild Traumatic Brain Injury on Postural Sway

Background: Mild Traumatic Brain Injury (mTBI) has been identified as a major public and military health concern both in the United States and worldwide. Characterizing the effects of mTBI on postural sway could be an important tool for assessing recovery from the injury. Methodology/Principal Findings: We assess postural sway by motion of the center of pressure (COP). Methods for data reduction include calculation of area of COP and fractal analysis of COP motion time courses. We found that fractal scaling appears applicable to sway power above about 0.5 Hz, thus fractal characterization is only quantifying the secondary effects (a small fraction of total power) in the sway time series, and is not effective in quantifying long-term effects of mTBI on postural sway. We also found that the area of COP sensitively depends on the length of data series over which the COP is obtained. These weaknesses motivated us to use instead Shannon and Renyi entropies to assess postural instability following mTBI. These entropy measures have a number of appealing properties, including capacity for determination of the optimal length of the time series for analysis and a new interpretation of the area of COP. Conclusions: Entropy analysis can readily detect postural instability in athletes at least 10 days post-concussion so that it appears promising as a sensitive measure of effects of mTBI on postural sway

Rate Effects on Timing, Key Velocity, and Finger Kinematics in Piano Performance

We examined the effect of rate on finger kinematics in goal-directed actions of pianists. In addition, we evaluated whether movement kinematics can be treated as an indicator of personal identity. Pianists' finger movements were recorded with a motion capture system while they performed melodies from memory at different rates. Pianists' peak finger heights above the keys preceding keystrokes increased as tempo increased, and were attained about one tone before keypress. These rate effects were not simply due to a strategy to increase key velocity (associated with tone intensity) of the corresponding keystroke. Greater finger heights may compensate via greater tactile feedback for a speed-accuracy tradeoff that underlies the tendency toward larger temporal variability at faster tempi. This would allow pianists to maintain high temporal accuracy when playing at fast rates. In addition, finger velocity and accelerations as pianists' fingers approached keys were sufficiently unique to allow pianists' identification with a neural-network classifier. Classification success was higher in pianists with more extensive musical training. Pianists' movement “signatures” may reflect unique goal-directed movement kinematic patterns, leading to individualistic sound

Applauding with Closed Hands: Neural Signature of Action-Sentence Compatibility Effects

BACKGROUND: Behavioral studies have provided evidence for an action-sentence compatibility effect (ACE) that suggests a coupling of motor mechanisms and action-sentence comprehension. When both processes are concurrent, the action sentence primes the actual movement, and simultaneously, the action affects comprehension. The aim of the present study was to investigate brain markers of bidirectional impact of language comprehension and motor processes. METHODOLOGY/PRINCIPAL FINDINGS: Participants listened to sentences describing an action that involved an open hand, a closed hand, or no manual action. Each participant was asked to press a button to indicate his/her understanding of the sentence. Each participant was assigned a hand-shape, either closed or open, which had to be used to activate the button. There were two groups (depending on the assigned hand-shape) and three categories (compatible, incompatible and neutral) defined according to the compatibility between the response and the sentence. ACEs were found in both groups. Brain markers of semantic processing exhibited an N400-like component around the Cz electrode position. This component distinguishes between compatible and incompatible, with a greater negative deflection for incompatible. Motor response elicited a motor potential (MP) and a re-afferent potential (RAP), which are both enhanced in the compatible condition. CONCLUSIONS/SIGNIFICANCE: The present findings provide the first ACE cortical measurements of semantic processing and the motor response. N400-like effects suggest that incompatibility with motor processes interferes in sentence comprehension in a semantic fashion. Modulation of motor potentials (MP and RAP) revealed a multimodal semantic facilitation of the motor response. Both results provide neural evidence of an action-sentence bidirectional relationship. Our results suggest that ACE is not an epiphenomenal post-sentence comprehension process. In contrast, motor-language integration occurring during the verb onset supports a genuine and ongoing brain motor-language interaction

Virtual time-to-contact of postural stability boundaries as a function of support surface compliance

This study investigated the hypothesis that virtual time-to-contact, which specifies the time to reach the functional stability boundary, is a variable controlled in the maintenance of upright posture. Three different levels of support surface compliance were used on a force platform (no foam, 5 cm of foam, and 15 cm of foam). The participant’s task was to stand still under each surface support condition both with and without vision. The stability boundary was determined for each set of conditions where the participant was required to lean as far as possible in all directions of the horizontal plane without losing stability. The results showed that the no vision conditions had a significantly larger center of pressure displacement than the vision conditions. No vision and increasing support surface compliance also increased the velocity of the center of pressure trajectory. The distribution of the radial displacement of the center of pressure showed relatively equal frequency over spatial location with no central tendency. The virtual time-to-contact with the stability boundary decreased as platform surface support became more compliant. Furthermore, the distribution of virtual time over the effective scaling range was a power law with a larger exponent in the more unstable no vision and increasing surface foam conditions. The findings provide additional evidence for the hypothesis that virtual time-to-contact with stability boundaries is a postural control variable that is regulated rather than the preservation of minimal motion around the center of the stability region as proposed in pendulum models of posture

Modulation and experience of external stimuli: toward a science of experience and interoception

The concept of interoception can be found in various writing over the past 100 or more years dating back to Sherrington, James and Lange. Professor György Ádám that made American scientists increasingly aware of the importance of interoception with his 1967 book Interoception and Behavior. In this article we want to discuss two areas of research from out laboratory that have been influenced from this perspective. First, we will focus on electrocortical correlates of error detection during visuo-motor task and examine the manner in which an individual becomes aware of making an error as well as the way in which this awareness directs behavior on an ongoing basis. Second, we will examine hypnotic modulation of the pain experience and describe the manner in which electrocortical processes reflect the modulation and experience of pain. In this discussion, we suggest the importance of the anterior cingulate in not only modulating these processes in particular but also in its more general role as an interface between the limbic system and the neocortex and the integration of cognitive with emotional stimuli