Cerebellar saccadic dysmetria is not equal in the two eyes

Experimental Brain Research - Differences in the saccadic dysmetria between the two eyes were examined in five trained monkeys. Dysmetria, produced by reversible lesions of the medial cerebellar...     

Relations of motor cortex neural discharge to kinematics of passive and active elbow movements in the monkey

1. Bedingham and Tatton recently reported that in cats trained not to resist imposed limb perturbations, some motor cortex (area 4) neurons responded predominantly to acceleration or jerk (the third derivative of position). The questions arose whether motor cortex neurons responding to higher derivatives of limb displacement exist in the primate in a resist-perturbation task and, if so, whether discharge of such neurons responds to the same kinematics in active (voluntary) movements. 2. To answer these questions we studied the discharge patterns of 203 motor cortex neurons that responded to torque pulse perturbations about the elbow and fired during active elbow flexions and extensions in four monkeys. Detailed analysis was performed on 66 neurons that responded reciprocally in both situations. 3. Reciprocal neurons discharged at short latency (20-40 ms) for one direction of arm perturbation. For the opposite direction they were initially silent or inhibited and then discharged at a variety of latencies but in apparent relation to limb kinematics. Based on the timing and overall pattern of their discharge the majority of neurons (68%) were classified as being acceleration-like. 4. Twenty-four (36%) of these reciprocal neurons had only sensory (kinematic)-like properties in active movements, i.e., they discharged after (and not before) movement onset. Discharge of these neurons followed the timing, but not the magnitude, of acceleration (20 neurons) or velocity (4 neurons). The discharge of these neurons also had a static component as the arm was held stationary. 5. Twenty-nine (44%) of reciprocal neurons commenced firing before movement onset for one direction of active movement, while for the opposite direction their discharge occurred after movement onset. Thus their discharge appeared to be muscle-related: both when the muscle was contracting as an agonist and stretched as an antagonist. 6. Although in these tasks discharge of MCNs could be generated either by sensory feedback or by motor responses, the strong response sensitivity of many neurons to acceleration supports the hypothesis that feedback based on higher derivatives of limb displacement could represent a "predictive" control system for accurate regulation of limb motion.     

Control of finger grip forces in overarm throws made by skilled throwers.

In an overarm throw, as the hand opens and the ball rolls along the fingers, the ball exerts a back force on the fingers. Previous studies suggested that skilled throwers compensate for this back force by producing an appropriate finger flexor torque to oppose the back force, but it was unclear how this is controlled by the CNS. We investigated whether the increase in finger flexor torque is timed precisely to occur late in the throw as the fingers open or whether the increase occurs throughout the throw to anticipate the increase in hand acceleration. Recreational ball players threw balls of different weights and diameters at different speeds from both a sitting and standing position while arm joint rotations were recorded with the search-coil technique. Force transducers were taped to the distal and middle phalanges of the middle finger and subjects released the ball from this finger. Passive forces on the finger were also recorded in "fake" throws in which the ball was taped to the finger and subjects did not grip the ball. These skilled throwers correctly anticipated the magnitude of the back force from the ball on the finger because the mean amplitude of finger extension did not increase in throws made with a large range of increasing back forces. This was achieved by subjects gripping the ball during the backswing with a force proportional to ball weight and intended ball speed (acceleration) and progressively increasing the grip force throughout the backswing and forward throw. The magnitude of this grip force during the forward throw was not affected by ball texture. After ball release from the fingertip, the finger flexed in proportion to the peak force on the finger before ball release. It is concluded, in a skilled fast overarm throw where large, fast-changing forces on the fingers result from the sum of motions at all arm joints, that finger flexor torque is progressively increased throughout the throw in an anticipatory (predictive) fashion to counteract the progressively increasing back force from the ball.     

Epithelial-myoepithelial carcinoma of the parotid gland: a case report and review of the cytological and histological features.

Epithelial-myoepithelial carcinoma (EMC) is a rare biphasic tumour of the salivary glands typically arising in the parotid. Fine needle aspiration cytology is widely used in the initial investigation of salivary gland swellings and whilst the cytological features of this tumour have been described they are not well recognized. This report describes the clinicopathological features of a case of epithelial-myoepithelial carcinoma of the parotid gland and highlights the importance of awareness of this tumour in the differential diagnosis of biphasic tumours on fine needle aspiration cytology.     

Increased variability in finger position occurs throughout overarm throws made by cerebellar and unskilled subjects.

We investigated the ability of cerebellar patients and unskilled subjects to control finger grip position and the amplitude of finger opening during a multijoint overarm throw. This situation is of interest because the appropriate finger control requires predicting the magnitude of back forces from the ball on the finger throughout the throw and generating the appropriate level and rate of change of finger flexor torque to oppose the back force. Cerebellar patients, matched controls, and unskilled subjects threw tennis balls and tennis-sized balls of different weights. In all cases angular positions of five arm segments in three dimension were recorded at 1,000 Hz with the search-coil technique as subjects threw from a seated position. When the hand was stationary, cerebellar patients showed a normal ability to grip the ball and open the fingers and drop the ball. In contrast, in overarm throws where a back force occurred on the fingers, cerebellar patients showed an abnormally large variability in amplitude of the change in finger position when gripping, in amplitude of finger opening, and in amplitude of the change in finger position 10 ms after ball release. This was not due to more trial-to-trial variation in throwing speed. When throwing balls of increasing weights, both controls and cerebellar patients had increasing finger flexions after ball release that indicated that, on average, both scaled finger force in proportion to ball weight during the throw. Unlike skilled controls, cerebellar patients showed a small (<20 degrees ) increase in the amplitude of finger opening with balls of increasing weight. However, neither the increase in variability of finger position nor the increase in finger amplitude with balls of increasing weight were unique cerebellar signs because both were observed to various degrees in unskilled throwers. It is concluded that in the absence of either normal cerebellar function or skill, the central neural activity that controls finger opening in throwing can increase finger flexor force to oppose an increase in back force from heavier balls and can open the fingers but cannot control finger force or finger opening precisely and consistently from throw to throw. These results fit with the idea that cerebellar disorders are greater in multijoint than single-joint movements because control of force is more complicated. They are also consistent with the hypothesis that the cerebellum produces skill in movement by reducing variability in the timing and force of muscle contractions.     

The effects of weak magnetic fields on radical recombination reactions in micelles

Purpose : To demonstrate the effects of weak magnetic fields (> ? 1 mT) on chemical reactions involving free radicals, in the context of possible effects of environmental electromagnetic radiation on biological systems. Materials and methods : Transient absorption, flash photolysis experiments have been performed to study the kinetics and yields of radical reactions. The triplet state of benzophenone has been used as a convenient source of radical pairs, whose identity is largely immaterial to the investigation of the so-called Low Field Effect. Hydrogen abstraction from surfactant molecules in micelles yields a pair of neutral radicals, one large and one small, in a region of restricted translational and rotational motion. Results : In alkyl sulphate and sulphonate micelles a weak field increases the concentration of free radicals that escape from the micelle to an extent that depends on the structure, dynamics and volume of the space in which the radical pairs are confined. The effect (up to 10%) is typically largest at 1-2 mT. Smaller effects are found for Brij and TX100 micelles. Conclusions : Low Field Effects depend strongly on the local environment of the radical pair. Larger effects than observed here might be expected for radicals formed from singlet (rather than triplet) precursors, as would be the case in biological reactions.