Journal of neurophysiology
-
Comparative Study
Kinematic and dynamic synergies of human precision-grip movements.
We analyzed the adaptability of human thumb and index finger movement kinematics and dynamics to variations of precision grip aperture and movement velocity. Six subjects performed precision grip opening and closing movements under different conditions of movement velocity and movement aperture (thumb and index finger tip-to-tip distance). Angular motion of the thumb and index finger joints was recorded with a CyberGlove and a three-dimensional biomechanical model was used for solving the inverse dynamics problem during precision grip movements, i.e., for calculating joint torques from experimentally obtained angular variations. ⋯ However, the adaptation to large aperture, achieved by an increase of the relative contribution of the proximal joints, was subject-invariant. At the level of movement dynamics, the adaptation of thumb-index finger movements to task constraints was similar among all subjects and required the linear scaling of joint torques, the synchronization of joint torques under high velocity conditions, and a flexible redistribution of joint torques between the proximal joint of the thumb and that of the index finger. This work represents one of the first attempts at calculating the joint torques during human precision-grip movements and indicates that the dynamic synergies seem to be remarkably simple compared with the synergies found for movement kinematics.
-
Comparative Study
Augmented mechanical response of muscle thin-fiber sensory receptors recorded from rat muscle-nerve preparations in vitro after eccentric contraction.
Unaccustomed strenuous exercise, especially that from eccentric muscular work, often causes muscle tenderness, which is a kind of mechanical hyperalgesia. We developed an animal model of delayed-onset muscle soreness (DOMS) from eccentric muscular contraction (ECC) in rats and demonstrated the existence of muscle tenderness by means of behavioral pain tests and c-Fos protein expression in the spinal dorsal horn. The purpose of the present study was to examine whether the sensitivities of muscle thin-fiber sensory receptors to mechanical, chemical, and thermal stimuli were altered after repetitive ECC in a rat model of DOMS. ⋯ In addition, the total number of evoked discharges during a ramp mechanical stimulus, taken as an index of the magnitude of the mechanical response, nearly doubled in the ECC preparations compared with the CTR [24.7 spikes (IQR; 14.2-37.1 spikes) in the CTR preparation vs. 54.2 spikes (IQR; 24.3-89.0 spikes) in the ECC, P < 0.001]. In contrast, the numbers of discharges induced by chemical (pH 5.5, lactic acid, adenosine triphosphate, and bradykinin) and thermal (cold and heat) stimuli were not different between the two preparations. These results suggest that augmentation of the mechanical response in muscle thin-fiber sensory receptors might be related to the muscle tenderness in DOMS after ECC.
-
Comparative Study
Kainate receptor-mediated synaptic transmission in the adult anterior cingulate cortex.
Kainate (KA) receptors are expressed widely in the CNS. However, little is known about their functional characterization, molecular identity, and role in synaptic transmission in the forebrain of adult mice. Patch-clamp recordings in genetically modified mice show that postsynaptic KA receptors contribute to fast synaptic transmission in pyramidal neurons in the anterior cingulate cortex (ACC), a forebrain region critical for higher-order cognitive brain functions such as memory and mental disorders. ⋯ High-frequency repetitive stimulation significantly facilitated the KA EPSCs. Genetic deletion of the GluR6 or GluR5 subunit significantly reduced, and GluR5 and 6 double knockout completely abolished, KA EPSCs and KA-activated currents in ACC pyramidal neurons. Our results show that KA receptors contribute to synaptic transmission in adult ACC pyramidal neurons and provide a synaptic basis for the physiology and pathology of KA receptors in ACC-related functions.
-
Comparative Study
An oscillatory hierarchy controlling neuronal excitability and stimulus processing in the auditory cortex.
EEG oscillations are hypothesized to reflect cyclical variations in the neuronal excitability, with particular frequency bands reflecting differing spatial scales of brain operation. However, despite decades of clinical and scientific investigation, there is no unifying theory of EEG organization, and the role of ongoing activity in sensory processing remains controversial. ⋯ This oscillatory hierarchy controls baseline excitability and thus stimulus-related responses in a neuronal ensemble. We propose that the hierarchical organization of ambient oscillatory activity allows auditory cortex to structure its temporal activity pattern so as to optimize the processing of rhythmic inputs.
-
Comparative Study
On the potential role of the corticospinal tract in the control and progressive adaptation of the soleus h-reflex during backward walking.
When untrained subjects walk backward on a treadmill, an unexpectedly large amplitude soleus H-reflex occurs in the midswing phase of backward walking. We hypothesized that activity in the corticospinal tract (CST) during midswing depolarizes the soleus alpha-motoneurons subliminally and thus brings them closer to threshold. To test this hypothesis, transcranial magnetic stimulation (TMS) was applied to the leg area of the motor cortex (MCx) during backward walking. ⋯ By contrast, no changes were observed in the timing or amplitude of soleus MEPs with training. Taken together, these observations make it unlikely that the motor cortex via the CST is involved in control of the H-reflex during the backward step cycle of untrained subjects nor in its progressive adaptation with training. Our observations raise the possibility that the large amplitude of H-reflex in untrained subjects and its adaptation with training are mainly due to control of presynaptic inhibition of Ia-afferents by other descending tracts.