Pyramidal Tract Neurons In Motor Cortex Research Articles

Different subtypes of motor cortex pyramidal tract neurons projects to red and pontine nuclei.

Pyramidal tract neurons (PTNs) are fundamental elements for motor control. However, it is largely unknown if PTNs are segregated into different subtypes with distinct characteristics. Using anatomical and electrophysiological tools, we analyzed in mice motor cortex PTNs projecting to red and pontine midbrain nuclei, which are important hubs connecting cerebral cortex and cerebellum playing a critical role in the regulation of movement. We reveal that the vast majority of M1 neurons projecting to the red and pontine nuclei constitutes different populations. Corticopontine neurons have higher conduction velocities and morphologically, a most homogeneous dendritic and spine distributions along cortical layers. The results indicate that cortical neurons projecting to the red and pontine nuclei constitute distinct anatomical and functional pathways which may contribute differently to sensorimotor integration.

High-Frequency Stimulation of the Subthalamic Nucleus Activates Motor Cortex Pyramidal Tract Neurons by a Process Involving Local Glutamate, GABA and Dopamine Receptors in Hemi-Parkinsonian Rats.

Deep brain stimulation (DBS) is widely used to treat advanced Parkinson’s disease (PD). Here, we investigated how DBS applied on the subthalamic nucleus (STN) influenced the neural activity in the motor cortex. Rats, which had the midbrain dopaminergic neurons partially depleted unilaterally, called the hemi-Parkinsonian rats, were used as a study model. c-Fos expression in the neurons was used as an indicator of neural activity. Application of high-frequency stimulation (HFS) upon the STN was used to mimic the DBS treatment. The motor cortices in the two hemispheres of hemi-Parkinsonian rats were found to contain unequal densities of c-Fos-positive (Fos+) cells, and STN-HFS rectified this bilateral imbalance. In addition, STN-HFS led to the intense c-Fos expression in a group of motor cortical neurons which exhibited biochemical and anatomical characteristics resembling those of the pyramidal tract (PT) neurons sending efferent projections to the STN. The number of PT neurons expressing high levels of c-Fos was significantly reduced by local application of the antagonists of non-N-methyl-D-aspartate (non-NMDA) glutamate receptors, gammaaminobutyric acid A (GABAA) receptors and dopamine receptors in the upper layers of the motor cortex. The results indicate that the coincident activations of synapses and dopamine receptors in the motor cortex during STN-HFS trigger the intense expression of c-Fos of the PT neurons. The implications of the results on the cellular mechanism underlying the therapeutic effects of STN-DBS on the movement disorders of PD are also discussed.

Feedback Modulation: A Window into Cortical Function

A recent study demonstrates involvement of primary motor cortex in task-dependent modulation of rapid feedback responses; cortical neurons resolve locally ambiguous sensory information, producing sophisticated responses to disturbances.

Direction-specific activities of dorsolateral prefrontal and motor cortex pyramidal tract neurons during visual tracking.

1. With two rhesus monkeys, activities of dorsolateral prefrontal cortex neurons (yt = 102) and rapidly conducting pyramidal tract neurons (PTNs) of the hand-arm motor area (n = 49) were compared for three kinds of single-step visual-tracking tasks. The manipulandum was a vertical handle, which the monkeys rotated 24’ from a central hold zone to a target hold zone by wrist flexion or extension. The first task was a delayed-response task (DR) in which the direction of the movement, that is, flexion or extension, was indicated by visual cues but was triggered, after a short delay period, by a visual go signal. The second task was a choice task (CT) in which wrist flexion or extension was triggered, after a short hold period, by both a go signal and a visual signal for direction of movement. The third task was a simple control task (ST) in which the same movement, either flexion or extension, was performed repeatedly after a go signal. 2. Only neurons with rate increase related to wrist movement were sampled. Two kinds of discharge patterns were differentiated, called bidirectional and unidirectional. When the rate increase was observed before and/ or during task movement, regardless of the direction of the movement, the pattern was bidirectional. When the rate increase occurred only for one direction (flexion or extension), with or without decrease for the other direction, the pattern was unidirectional. 3. During delayed responses 59 prefrontal neurons showed bidirectional activity and 43 neurons showed unidirectional activity before and during task movement. About half of these prefrontal neurons showed a gradually developing rate change in the later phase of the delay period, either bidirectionally or unidirectionally. It started about 0.31.2 s earlier than the go signal. PTNs showed similar changes. Thirty-two PTNs were activated unidirectionally and 18 PTNs were activated bidirectionally. About one-fourth of the PTNs showed a gradually developing rate change in the later phase of the delay period. Its temporal course was similar to that of prefrontal neurons. 4. During a choice task occurrences of activations of both prefrontal neurons and PTNs before and during movement were less frequent than during the delayed-response tasks. Gradually developing activation of prefrontal neurons also occurred with less frequency. Gradually developing activation of PTNs was not seen. 5. During simple control tasks gradually developing activation before the go signal persisted. 6. It is concluded that prior to voluntary movement there is neuronal activity specific to movement direction, in addition to nonspecific activity, in the prefrontal cortex. Movement-related activities may be involved in the effective execution of goal-directed voluntary movement.

Relation of size and activity of motor cortex pyramidal tract neurons during skilled movements in the monkey

Activity of motor cortex pyramidal tract neurons (PTNs) was recorded in monkeys making large (20 degrees), high velocity and small (1 to 2 degrees), low velocity pronation-supination arm movements in a visual pursuit-tracking paradigm. Antidromic response latencies (ADLs) or PTNs were examined in relation to PTN modulation with the large and small movements to test the hypothesis that PTNs would exhibit a "size principle" analogous to that of spinal cord motoneurons. It was found that smaller PTNs (i.e., those having longer ADLs) discharged just as strongly with small, slow movements as with large, fast movements, while about one-third of the larger PTNs (even those selected for a significant relation to small movement) discharged more intensely with the large movement. Another analysis dealing with PTNs in a selected set of penetrations in an area focal for pronation-supination showed that PTNs with longer ADLs (greater than 1 msec) were more likely to reach maximum frequency with small, slow movement. There was, however, much overlap in the behavior of small and large PTNs, and while there was a statistically significant relation between size and movement-related activity of PTNs, there did not seem to be a "size principle" in the strict sense that this term has been used with reference to spinal cord motoneurons.

Mediation of quick motor responses by motor cortex pyramidal tract neurons in the monkey

Mediation of quick motor responses by motor cortex pyramidal tract neurons in the monkey

Relation of motor cortex neurons to precisely controlled and ballistic movements

A visual pursuit-tracking paradigm was used for training monkeys to position a handle within a small zone and rotate it by pronation-supination movements. Motor cortex unit discharge was examined in relation to movements carried out in this situation, with particular attention to large ballistic movements as compared to small precisely controlled movements. Intense unit discharge was found to occur with even the smallest movements made to achieve accurate positioning of the handle. Within the group of motor cortex pyramidal tract neurons (PTNs), slowly conducting tonically discharging PTNs showed the most selective relations to these small precisely controlled movements.

Reflex and intended responses in motor cortex pyramidal tract neurons of monkey.

1. Monkeys were trained to react to an arm perturbation according to an instruction delivered prior to the perturbation. There were two possible instructions (push or pull), and monkeys learned to respond accordingly regardless of the direction (push or pull) of the triggering perturbation. 2. Pyramidal tract neurons (PTNs) in contralateral motor cortex arm area responded to the triggering perturbation with two dissociable components: 1) a relatively short-latency (20-25 ms) reflex component which depended on the direction of the perturbation, and 2) a longer latency (40-50 ms) intended component which depended on the prior instruction. 3. Intended PTN discharge could occur in arm area with latencies of 50 ms even following arm perturbations whose initial reflex effects on the PTN were inhibitory. 4. Intended PTN responses triggered by perturbations of the appropriate body part occur at shorter latencies than intended PTN responses triggered by auditory or visual stimuli. These short-latency intended PTN responses may play a role in thsshort-latency but volitionally controlled limb movements occurring in response to limb perturbations.