Cortical networks produce three distinct 7-12 Hz rhythms during single sensory responses in the awake rat.

Cortical rhythms in the alpha/mu frequency range (7-12 Hz) have been variously related to "idling," anticipation, seizure, and short-term or working memory. This overabundance of interpretations suggests that sensory cortex may be able to produce more than one (and even more than two) distinct alpha/mu rhythms. Here we describe simultaneous local field potential and single-neuron recordings made from primary sensory (gustatory) cortex of awake rats and reveal three distinct 7-12 Hz de novo network rhythms within single sessions: an "early," taste-induced approximately 11 Hz rhythm, the first peak of which was a short-latency gustatory evoked potential; a "late," significantly lower-frequency (approximately 7 Hz) rhythm that replaced this first rhythm at approximately 750-850 ms after stimulus onset (consistently timed with a previously described shift in taste temporal codes); and a "spontaneous" spike-and-wave rhythm of intermediate peak frequency (approximately 9 Hz) that appeared late in the session, as part of a oft-described reduction in arousal/attention. These rhythms proved dissociable on many grounds: in addition to having different peak frequencies, amplitudes, and shapes and appearing at different time points (although often within single 3 s snippets of activity), the early and late rhythms proved to have completely uncorrelated session-to-session variability, and the spontaneous rhythm affected the early rhythm only (having no impact on the late rhythm). Analysis of spike-to-wave coupling suggested that the early and late rhythms are a unified part of discriminative taste process: the identity of phase-coupled single-neuron ensembles differed from taste to taste, and coupling typically lasted across the change in frequency. These data reveal that even rhythms confined to a narrow frequency band may still have distinct properties.

Effect of gravity on robot-assisted motor training after chronic stroke: a randomized trial.

OBJECTIVES: To determine the efficacy of 2 distinct 6-week robot-assisted reaching programs compared with an intensive conventional arm exercise program (ICAE) for chronic, stroke-related upper-extremity (UE) impairment. To examine whether the addition of robot-assisted training out of the horizontal plane leads to improved outcomes. DESIGN: Randomized controlled trial, single-blinded, with 12-week follow-up. SETTING: Research setting in a large medical center. PARTICIPANTS: Adults (N=62) with chronic, stroke-related arm weakness stratified by impairment severity using baseline UE motor assessments. INTERVENTIONS: Sixty minutes, 3 times a week for 6 weeks of robot-assisted planar reaching (gravity compensated), combined planar with vertical robot-assisted reaching, or intensive conventional arm exercise program. MAIN OUTCOME MEASURE: UE Fugl-Meyer Assessment (FMA) mean change from baseline to final training. RESULTS: All groups showed modest gains in the FMA from baseline to final with no significant between group differences. Most change occurred in the planar robot group (mean change ± SD, 2.94 ± 0.77; 95% confidence interval [CI], 1.40-4.47). Participants with greater motor impairment (n=41) demonstrated a larger difference in response (mean change ± SD, 2.29 ± 0.72; 95% CI, 0.85-3.72) for planar robot-assisted exercise compared with the intensive conventional arm exercise program (mean change ± SD, 0.43 ± 0.72; 95% CI, -1.00 to 1.86). CONCLUSIONS: Chronic UE deficits because of stroke are responsive to intensive motor task training. However, training outside the horizontal plane in a gravity present environment using a combination of vertical with planar robots was not superior to training with the planar robot alone.

Predictors and brain connectivity changes associated with arm motor function improvement from intensive practice in chronic stroke.

Background and Purpose: The brain changes that underlie therapy-induced improvement in motor function after stroke remain obscure. This study sought to demonstrate the feasibility and utility of measuring motor system physiology in a clinical trial of intensive upper extremity rehabilitation in chronic stroke-related hemiparesis. Methods: This was a substudy of two multi-center clinical trials of intensive robotic arm therapy in chronic, significantly hemiparetic, stroke patients. Transcranial magnetic stimulation was used to measure motor cortical output to the biceps and extensor digitorum communus muscles. Magnetic resonance imaging (MRI) was used to determine the cortical anatomy, as well as to measure fractional anisotropy, and blood oxygenation (BOLD) during an eyes-closed rest state. Region-of-interest time-series correlation analysis was performed on the BOLD signal to determine interregional connectivity. Functional status was measured with the upper extremity Fugl-Meyer and Wolf Motor Function Test. Results: Motor evoked potential (MEP) presence was associated with better functional outcomes, but the effect was not significant when considering baseline impairment. Affected side internal capsule fractional anisotropy was associated with better function at baseline. Affected side primary motor cortex (M1) activity became more correlated with other frontal motor regions after treatment. Resting state connectivity between affected hemisphere M1 and dorsal premotor area (PMAd) predicted recovery.  Conclusions: Presence of motor evoked potentials in the affected motor cortex and its functional connectivity with PMAd may be useful in predicting recovery. Functional connectivity in the motor network shows a trends towards increasing after intensive robotic or non-robotic arm therapy. Clinical Trial Registration URL:  http://www.clinicaltrials.gov. Unique identifiers:  CT00372411 & NCT00333983.

Psychophysiological support of increasing attentional reserve during the development of a motor skill.

The aim of this study was to determine the relationship between motor skill and attentional reserve. Participants practiced a reaching task with the dominant upper extremity, to which a distortion of the visual feedback was applied, while a control group performed the same task without distortion. Event-related brain potentials (ERPs), elicited by auditory stimuli were recorded throughout practice. Performance, as measured by initial directional error, was initially worse relative to controls and improved over trials. Analyses of the ERPs revealed that exogenous components, N1 and P2, were undifferentiated between the groups and did not change with practice. Notably, amplitude of the novelty P3 component, an index of the involuntary orienting of attention, was initially attenuated relative to controls, but progressively increased in amplitude over trials in the learning group only. The results provide psychophysiological evidence that attentional reserve increases as a function of motor skill acquisition.