Activity Of Pyramidal Tract Neurons Research Articles

Diverse operant control of different motor cortex populations during learning

During motor learning,1 as well as during neuroprosthetic learning,2-4 animals learn to control motor cortex activity in order to generate behavior. Two different populations of motor cortex neurons, intra-telencephalic (IT) and pyramidal tract (PT) neurons, convey the resulting cortical signals within and outside the telencephalon. Although a large amount of evidence demonstrates contrasting functional organization among both populations,5,6 it is unclear whether the brain can equally learn to control the activity of either class of motor cortex neurons. To answer this question, we used a calcium-imaging-based brain-machine interface (CaBMI)3 and trained different groups of mice to modulate the activity of either IT or PT neurons in order to receive a reward. We found that the animals learned to control PT neuron activity faster and better than IT neuron activity. Moreover, our findings show that the advantage of PT neurons is the result of characteristics inherent to this population as well as their local circuitry and cortical depth location. Taken together, our results suggest that the motor cortex is more efficient at controlling the activity of pyramidal tract neurons, which are embedded deep in the cortex, and relaying motor commands outside the telencephalon.

Similar Motor Cortical Control Mechanisms for Precise Limb Control during Reaching and Locomotion.

Throughout the course of evolution there has been a parallel development of the complexity and flexibility of the nervous system and the skeletomuscular system that it controls. This development is particularly evident for the cerebral cortical areas and the transformation of the use of the upper limbs from a purely locomotor function to one including, or restricted to, reaching and grasping. This study addresses the issue of whether the control of reaching has involved the development of new cortical circuits or whether the same neurons are used to control both locomotion and reaching. We recorded the activity of pyramidal tract neurons in the motor cortex of the cat both during voluntary gait modifications and during reaching. All cells showed generally similar patterns of activity in both tasks. More specifically, we showed that, in many cases, cells maintained a constant temporal relationship to the activity of synergistic muscle groups in each task. In addition, in some cells the relationship between the intensity of the cell discharge activity and the magnitude of the EMG activity was equally constant during gait modifications and reaching. As such, the results are compatible with the hypothesis that the corticospinal circuits used to control reaching evolved from those used to precisely modify gait.

Activity of pyramidal tract neurons in the cat during standing and walking on an inclined plane

To keep balance when standing or walking on a surface inclined in the roll plane, the cat modifies its body configuration so that the functional length of its right and left limbs becomes different. The aim of the present study was to assess the motor cortex participation in the generation of this left/right asymmetry. We recorded the activity of fore- and hindlimb-related pyramidal tract neurons (PTNs) during standing and walking on a treadmill. A difference in PTN activity at two tilted positions of the treadmill (+/- 15 deg) was considered a positional response to surface inclination. During standing, 47% of PTNs exhibited a positional response, increasing their activity with either the contra-tilt (20%) or the ipsi-tilt (27%). During walking, PTNs were modulated in the rhythm of stepping, and tilts of the supporting surface evoked positional responses in the form of changes to the magnitude of modulation in 58% of PTNs. The contra-tilt increased activity in 28% of PTNs, and ipsi-tilt increased activity in 30% of PTNs. We suggest that PTNs with positional responses contribute to the modifications of limb configuration that are necessary for adaptation to the inclined surface. By comparing the responses to tilts in individual PTNs during standing and walking, four groups of PTNs were revealed: responding in both tasks (30%); responding only during standing (16%); responding only during walking (30%); responding in none of the tasks (24%). This diversity suggests that common and separate cortical mechanisms are used for postural adaptation to tilts during standing and walking.

Influences of sensory input from the limbs on feline corticospinal neurons during postural responses

The dorsal-side-up body posture of standing quadrupeds is maintained by coordinated activity of all limbs. Somatosensory input from the limbs evokes postural responses when the supporting surface is perturbed. The aim of this study was to reveal the contribution of sensory inputs from individual limbs to the posture-related modulation of pyramidal tract neurons (PTNs) arising in the primary motor cortex. We recorded the activity of PTNs from the limb representation of motor cortex in the cat maintaining balance on a platform periodically tilted in the frontal plane. Each PTN was recorded during standing on four limbs, and when two or three limbs were lifted from the platform and thus did not signal its displacement to motor cortex. By comparing PTN responses to tilts in different tests we found that the amplitude and the phase of the response in the majority of them were determined primarily by the sensory input from the corresponding contralateral limb. In a portion of PTNs, this input originated from afferents of the peripheral receptive field. Sensory input from the ipsilateral limb, as well as input from limbs of the other girdle made a much smaller contribution to the PTN modulation. These results show that, during postural activity, a key role of PTNs is the feedback control of the corresponding contralateral limb and, to a lesser extent, the coordination of posture within a girdle and between the two girdles.

Role of GABA A inhibition in modulation of pyramidal tract neuron activity during postural corrections.

In a previous study we demonstrated that the activity of pyramidal tract neurons (PTNs) of the motor cortex is modulated in relation to postural corrections evoked by periodical tilts of the animal. The modulation included an increase in activity in one phase of the tilt cycle and a decrease in the other phase. It is known that the motor cortex contains a large population of inhibitory GABAergic neurons. How do these neurons participate in periodic modulation of PTNs? The goal of this study was to investigate the role of GABAA inhibitory neurons of the motor cortex in the modulation of postural-related PTN activity. Using extracellular electrodes with attached micropipettes, we recorded the activity of PTNs in cats maintaining balance on a tilting platform both before and after iontophoretic application of the GABAA receptor antagonists gabazine or bicuculline. The tilt-related activity of 93% of PTNs was affected by GABAA receptor antagonists. In 88% of cells, peak activity increased by 75 ± 50% (mean ± SD). In contrast, the trough activity changed by a much smaller value and almost as many neurons showed a decrease as showed an increase. In 73% of the neurons, the phase position of the peak activity did not change or changed by no more than 0.1 of a cycle. We conclude that the GABAergic system of the motor cortex reduces the posture-related responses of PTNs but has little role in determining their response timing.

Activity of Pyramidal Tract Neurons in the Cat During Postural Corrections

The dorsal side-up body orientation in quadrupeds is maintained by a postural control system. We investigated participation of the motor cortex in this system by recording activity of pyramidal tract neurons (PTNs) from limb representations of the motor cortex during postural corrections. The cat was standing on the platform periodically tilting in the frontal plane, and maintained equilibrium at different body configurations: with the head directed forward (symmetrically alternating loading of the left and right fore limbs), or with the head voluntary turned to the right or to the left (asymmetrical loading). We found that postural corrective responses to tilts included an increase of the contact forces and activity of limb extensors on the side moving down, and their decrease on the opposite side. The activity of PTNs was strongly modulated in relation to the tilt cycle. Phases of activity of individual PTNs were distributed over the cycle. Thus the cortical output mediated by PTNs appeared closely related to a highly automatic motor activity, the maintenance of the body posture. An asymmetrical loading of limbs, caused by head turns, resulted in the corresponding changes of motor responses to tilts. These voluntary postural modifications were also well reflected in the PTNs' activity. The activity of a part of PTNs correlated well with contact forces, in some others with the limb muscle activity; in still others no correlation with these variables was observed. This heterogeneity of the PTNs population suggests a different functional role of individual PTNs.

Local Application of Dopamine Inhibits Pyramidal Tract Neuron Activity in the Rodent Motor Cortex

Cortical neurons respond in a variety of ways to locally applied dopamine, perhaps because of the activation of different receptors within or among subpopulations of cells. This study was conducted to assess the effects of dopamine and the receptor subtypes that mediate the responses of a specific population of neurons, the pyramidal tract neurons (PTNs) in the rodent motor cortex. The specific subfamilies of dopamine receptors expressed by PTNs also were determined. PTNs were identified by antidromic stimulation in intact animals. Extracellular recordings of their spontaneous activity and glutamate-induced excitation were performed with multi-barrel pipettes to allow simultaneous recording and iontophoresis of several drugs. Prolonged (30 s) application of dopamine caused a progressive, nonlinear decrease in spontaneous firing rates for nearly all PTNs, with significant reductions from baseline spontaneous activity (71% of baseline levels) occurring between 20 and 30 s of iontophoresis. The D1 selective (SCH23390) and the D2 selective (eticlopride) antagonists were both effective in blocking dopamine-induced inhibition in nearly all PTNs. Mean firing levels were maintained within 3% of baseline levels during co-application of the D1 antagonist with dopamine and within 11% of baseline levels during co-application of the D2 antagonist and dopamine. SCH23390 was ineffective however, in 2 of 16 PTNs, and eticlopride was ineffective in 3 PTNs. The dopamine blockade by both antagonists in most neurons, along with the selective blockade by one, but not the other antagonist in a few neurons indicate that the overall population of PTNs exhibits a heterogeneous expression of dopamine receptors. The firing rate of PTNs was significantly enhanced by iontophoresis of glutamate (mean = 141% of baseline levels). These increases were attenuated significantly (mean= 98% of baseline) by co-application with dopamine in all PTNs, indicating dopaminergic interactions with glutamate transmission. The expression of dopamine receptors was studied with dual-labeling techniques. PTNs were identified by retrograde labeling with fast blue and the D1a, D2, or D5 receptor proteins were stained immunohistochemically. Some, but not all PTNs, showed labeling for D1a, D2, or D5 receptors. The D1a and D2 receptor immunoreactivity was observed primarily in the somata of PTNs, whereas D5 immunoreactivity extended well into the apical dendrites of PTNs. In accordance with findings of D1 and D2 receptor antagonism of dopamine's actions, the identification of three DA receptor subtypes on PTNs suggests that dopamine can directly modulate PTN activity through one or more receptor subtypes.

Dopaminergic modulation of transcallosal activity of cat motor cortical neurons

The effects of dopamine (DA) and its antagonists on the transcallosal activity of pyramidal tract neurons (PTNs) and non-PTNs in the anesthetized cat motor cortex were studied with iontophoretic applications; dopamine, SCH 23390 (D1 antagonist), sulpiride (D2 antagonist) and haloperidol. Neuronal activity was recorded with a multi-barreled glass microelectrode. Transcallosal neuronal activity was evoked by stimulation of the contralateral motor cortex. The number of spikes thus activated was counted for the control and test conditions after application of each drug: (1) dopamine application decreased the number of spikes evoked by transcallosal stimulation; (2) application of SCH 23390, sulpiride and haloperidol restored these decreased spike numbers to the control level; (3) latency of neuronal response to transcallosal stimulation was not affected by the application of either DA, SCH 23390, sulpiride or haloperidol; and (4) there was no significant difference between PTNs and non-PTNs in the manner of response to DA and its antagonist applications. Our conclusion is that dopamine modulated the transcallosal neuronal response in the cat motor cortex in a suppressive manner. This fact suggested that interhemispheric neuronal communications could be subjected to suppressive modification by the dopaminergic system.

Dendritic action potentials of pyramidal tract neurons in the cat sensorimotor cortex

The intracellular activity of pyramidal tract neurons was studied during electrical stimulation of ventrolateral and ventroposterolateral thalamic nuclei in acute experiments on cats immobilized by myorelaxants. Somatic action potentials were observed and spontaneous spikes were also produced by single and rhythmic stimulation of the thalamic nuclei at the rate of 8–14 Hz, by iontophoretic application of strychnine, and by intracellular depolarizing current pulses. These potentials had a relatively low and variable amplitude of 5–60 mV and are presumed to be dendritic action potentials. It is postulated that these variable potentials arise in the dendrites of pyramidal neurons with multiple zones generating such activity. No interaction was observed where somatic and dendritic action potentials occur simultaneously. The possible functional role of dendritic action potentials is discussed.

Low threshold motor effects produced by stimulation of area preinsularis (2 pr.i) of the secondary sensory cortex in the cat; input-output relationship.

Intracortical microstimulation (ICMS) delivered to area 2 perinsularis (area 2 pr. i) of the second somatosensory cortex, SII, elicited contralateral distal limb movements with threshold currents as low as 2 microA. The effective sites for a particular movement were located in a small area within the depth of the cortex extending along the direction of the radial fibers. Neurons in an area for a particular movement generally received peripheral input from the skin overlying the muscle to which the area projected. ICMS in area 2 pr.i produced powerful monosynaptic as well as disynaptic activation of pyramidal tract neurons, suggesting that the effect was mediated by the pyramidal tract. Ablation of the motor cortex did not eliminate or otherwise reduce the low threshold responses from area 2 pr.i suggesting that the described effect is independent of the motor cortex.

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.

Correlation of monkey pyramidal tract neuron activity to movement velocity in rapid wrist flexion movement

The activity of 41 pyramidal tract neurons (PTNs) within the hand-arm area of the monkey motor cortex was studied during a rapid wrist flexion movement at specified velocities. The discharge rate during the movement showed significant correlations to the movement velocity in 21 PTNs, but the rate before the movement onset did not show correlations. Therefore the PTN activity before the movement onset in the rapid wrist flexion is not coding the velocity of the 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.

Monkey pyramidal tract neurons and changes of movement parameters in visual tracking

During a single-step visual tracking task of monkeys, parametric changes of the wrist extension-flexion movement and related discharge rate changes of pyramidal tract neurons (PTNs) of hand-arm motor area were studied. The task consisted of preparatory, precontraction, contraction and target periods. If the displacement amplitude was changed from narrow (10–20°) to moderate (40°) range, peak velocity, peak acceleration and contraction period increased linearly but precontraction period decreased slightly. In 61 movement-related PTNs, no linear relationships were found between PTN discharge rate during precontraction or contraction period and displacement amplitude, velocity, acceleration, precontraction period or contraction period. In less than 20% of PTNs, however, correlations between PTN discharge rate during precontraction period and velocity or acceleration were found in the moderate range task. It occurred less frequently in narrow range task. It is said in a visual tracking task that PTN activity is not dependent upon factors related to the task parameters, such as velocity, acceleration. Possible related factors were discussed.

Antidromic activation of pyramidal tract neurons following topical penicillin application. A possible mechanism in the generation of paroxysmal events

Pyramidal tract (PT) neurons identified through antidromic stimulation were recorded with extracellular multibarrelled microelectrodes in the rat motor cortex. Topical application of small amounts of penicillin to the PT fibers at the medullary level induced the generation of action potentials (APs) near the injection site. These APs, which propagated antidromically to the cortex, could be characterized by collision test. It is suggested that a similar phenomenon may occur on intracortical collaterals of PT fibers within a cortical penicillin focus. Such ‘ectopic’ AP generation may contribute significantly to the generation of paroxysmal events.

Brain mechanisms in motor control

Publisher Summary This chapter describes the brain mechanisms in motor control. In primates, a zone of cerebral cortex lying anterior to the central fissure contains a set of neurons whose axons pass without interruption to the spinal cord through a nerve bundle named the pyramidal tract and the neurons of this tract are called pyramidal tract neurons (PTNs). In the spinal cord, the axon terminals of PTNs end both in the interneuronal pool and on alpha and gamma motoneurons. Studies of PTN discharge in monkeys that are able to carry out differing movements depending upon the instructions they have received have revealed that one factor influencing motor cortex PTN discharge frequency in the absence of overt muscular contraction is the intention to move. The variation in PTN activity in relation to intention to move is seen even before any muscular activity occurs. It is found that when a monkey has learned that a particular signal means he should flex his elbow; PTNs adopt a pattern of discharge corresponding to the intention to flex. A different pattern of PTN discharge frequency is adopted if the monkey receives a signal instructing him to extend.

Inhibition in the neurons of the somatosensory cortex and the possibility of intracortical propagation of excitation

Extra- and intracellular leads were used to study the reactions of neurons in the pyramidal tract (PT) of the cat brain to antidromic and afferent effects. It was shown that afferent activation of PT neurons proceeds heterogeneously. Three types of PT neurons were identified, successively involved in the impulse response to afferent stimulation. By means of paired stimuli we determined the heterogeneous changes in sensitivity of late reacting PT neurons. It was found that, under certain conditions, the different IPSP evoked by afferent stimulation or PT stimulation do not prevent the appearance of impulse responses to secondary synaptic activation. A conclusion was drawn from these experiments on the localization of the excitatory intracortical terminals on the somas of the PT neurons and on the limited effect of inhibitory processes upon intracortical propagation of the afferent signal reaching the cortex. A functional scheme of intracortical PT neuron links is presented.

Multisensory activation of pyramidal tract neurons in the cat

Extracellular unit recordings were made of the responses of pericruciate neurons to photic, auditory, and forepaw stimulation in chloralose-anesthetized cats. More than 70% of pyramidal tract (PT) neurons was activated by two or more different sensory modalities, whereas about 40% of other neurons had such sensory convergence. The majority of the responsive pericruciate, neurons was located in the lower one-half of the cortex. During sensory activation PT activity was found to precede the cortical-evoked response. The majority of the multisensory PT cells belonged to the “fast” group with conduction velocities between 25 and 50 m/sec. The results suggest that multisensory activation of certain pericruciate neurons provides a means of rapidly producing a state of “readiness to act” in the spinal cord.

Activity of pyramidal tract neurons during postural fixation.

Activity of pyramidal tract neurons during postural fixation.

Activation of pyramidal tract neurons by ipsilateral cutaneous stimuli.

ArticlesACTIVATION OF PYRAMIDAL TRACT NEURONS BY IPSILATERAL CUTANEOUS STIMULIH. D. Patton, A. L. Towe, and T. T. KennedyH. D. Patton, A. L. Towe, and T. T. KennedyPublished Online:01 Jul 1962https://doi.org/10.1152/jn.1962.25.4.501MoreSectionsPDF (3 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByInfluence of anesthesia on spontaneous activity and receptive field size of single units in rat Sm1 neocortexExperimental Neurology, Vol. 99, No. 2Ipsilateral and contralateral SEP components following median nerve stimulation: Effects of interfering stimuli applied to the contralateral handElectroencephalography and Clinical Neurophysiology, Vol. 64, No. 3Trigeminal evoked potentials in humansElectroencephalography and Clinical Neurophysiology, Vol. 48, No. 5Transcortical reflexes and focal motor epilepsyElectroencephalography and Clinical Neurophysiology, Vol. 45, No. 3Functional subsets of neurons in somatosensory thalamus of the catExperimental Neurology, Vol. 58, No. 2Inhibition of unit activity in the hypothalamic paraventricular nucleus following antidromic activationBrain Research, Vol. 42, No. 2Extracellular potential fields of single PT-neuronsBrain Research, Vol. 36, No. 2Organization of visual input in cat motor-sensory cortexExperimental Neurology, Vol. 33, No. 3The effects of brain lesions on the performance of bilateral arm movementsNeuropsychologia, Vol. 9, No. 1Relationships between positive-negative extracellular potentials and intracellular potentials in pyramidal tract neuronsElectroencephalography and Clinical Neurophysiology, Vol. 30, No. 1The influence of hypnotics and tranquillizers on some evoked cortical potentialsNeuropharmacology, Vol. 10, No. 1Interhemispheric influences on sensorimotor neuronsExperimental Neurology, Vol. 28, No. 1Some properties of antidromically activated units in the paraventricular nucleus of the hypothalamusExperimental Neurology, Vol. 26, No. 2Electrophysiological maturation of the pyramidal tract in the post-natal rabbitElectroencephalography and Clinical Neurophysiology, Vol. 26, No. 6Differential activity among wide-field neurons of the cat postcruciate cerebral cortexExperimental Neurology, Vol. 20, No. 4Hemispheric specialization: A possible clue to mechanismNeuropsychologia, Vol. 6, No. 1Functional characteristics of neurons in the lateral reticular nucleus with reference to localized cerebellar potentialsExperimental Neurology, Vol. 18, No. 2Reaction time and conducting pathways of the brainNeuropsychologia, Vol. 4, No. 2Laterality effects in somesthesis following cerebral commissurotomy in manNeuropsychologia, Vol. 1, No. 3Properties of the pyramidal system in the catExperimental Neurology, Vol. 8, No. 3Intrathalamic regulation of activity in a cerebellocortical projection pathwayExperimental Neurology, Vol. 6, No. 6 More from this issue > Volume 25Issue 4July 1962Pages 501-514 https://doi.org/10.1152/jn.1962.25.4.501PubMed14484429History Published online 1 July 1962 Published in print 1 July 1962 Metrics