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At least 433 records · Page 24Linked to original sources
PubMed1978

Operant control of pyramidal tract neurons: the role of spinal dorsal columns.

A monkey was trained to control the firing patterns of precentral pyramidal tract neurons. The operant task was for the monkey to produce consecutive interspike intervals (ISI) within a requisite range, or target. The mean time off-target (error) is used to quantify the accuracy of control the monkey could assert over each PTN. Following partial destruction of the dorsal funiculi the number of PTNs driven by peripheral stimuli greatly decreased. Those PTNs which remained responsive to peripheral stimuli were as accurately controlled as those tested before column section, whereas, those PTNs unresponsive to peripheral stimuli were significantly less accurately controlled. The conclusion is that the monkey relies heavily upon proprioceptive feedback to operantly control precentral PTNs.

Acoustic Stimulation↗
PubMed1978

Dorsolateral prefrontal cortex lesions and discrimination of movement-produced cues by rhesus monkeys.

Rhesus monkeys were trained on a conditional discrimination in which sequences of either 32 or 64 lever presses served as discriminative stimuli. For half the subjects, reinforcement was contingent upon choice of a red response key following a sequence of 32 presses (FR 32), and a white key after FR 64, with the position of the two key colors randomized across trials. The remaining subjects were reinforced for left key presses after FR 64, and right key presses after FR 32, with key color again randomized across trials. Ablation of dorsolateral prefrontal cortex resulted in postoperative deficits in all subjects, although 6 of 8 eventually remastered the task. This recovery was investigated in a second experiment, in which psychophysical functions were generated by varying the length of the shorter FR. Although dorsolateral lesions again produced a severe disruption in performance, the post-operative functions eventually obtained were identical to the preoperative functions. This pattern of marked impairment in retention of fixed ratio discriminations, but no change in asymptotic capacity, suggests participation of dorsolateral prefrontal cortex in processing kinesthetic information, possibly analogous to the role of inferior temporal cortex in processing visual information.

Animals↗
PubMed1979

A proposed natural geometry of recovery from akinesia in the lateral hypothalamic rat.

The Eshkol-Wachmann movement notation is used to analyze and describe neurological recovery from the akinesia caused by severe bilateral lateral hypothalamic (LH) damage in rats. Exploratory movement recovers along several relatively independent dimensions which appear successively. First, lateral head scanning movements recover. At about the same time or later, longitudinal (backward-forward) head scans appear. After movements along these two dimensions increase in amplitude and involve the whole body, vertical (dorsal-ventral) head scans with snout contact (along vertical surfaces) typically appear, and increase gradually in amplitude. Later, vertical rearing without snout contact emerges. Recovery proceeds cephalocaudally, as more caudal limb and body segments are recruited along each of the above dimensions separately. LH rats show delayed recruitment of caudal limb and body segments ('strait-jacket phenomenon'). Support of the body and management of limb and body segments' contact with the ground also recover relatively independently, in a proximodistal fashion. In recovery, arrests between bouts of activity become shorter. Movement first becomes organized in relation to the animals' own body, and only much later, in relation to the environment. In each sequence of movement after pronounced immobility, the rat recapitulates the process of recovery; and, any time it starts to move, it repeats the movements at a particular amplitude several times until there is an increase to the next larger size movement ('warm-up' phenomenon). These regularities explain the apparently bizarre stereotyped behavior in partial enclosures ('behavioral traps') seen in LH rats recovering from akinesia. They also explain some aspects of exploration in rats and normal social behavior of wild animals, particularly in situations involving fear and conflict.

Animals↗
PubMed1979

Changes in canine postural control after injury to anterior vermal cerebellum.

For a preliminary exploration of cerebellar influences on postural control, dogs were trained to stand quietly erect. Posture was perturbed by sinusoidal movement of the supporting table while the dogs were sighted and while they were blindfolded or stimulated by sinusoidal optokinetic stimuli. Postural responses were evaluated by measuring the relative amplitude of pelvis movement over a series of perturbing frequencies; frequency response descriptions were derived. Lesions of the cerebellar vermis in 3 dogs involved the cortex of lobules V and VI, of lobules IV, V and VI, and of lobules IV--VII plus damage to the medial portion of nucleus fastigius. The two smaller lesions degraded the animal's tracking ability under all three conditions temporarily with extensive but incomplete compensation in 14--21 days. The larger lesion effectively and permanently eliminated the animal's ability to track table or visual field motion. Elimination of visual cues by blindfolding or perturbing the posture with optokinetic stimuli significantly exaggerated the control deficiencies produced by the lesions. It is concluded that the visual input to the cerebellar vermis finds expression through postural control channels.

Animals↗
PubMed1979

The relationship between dendritic growth of cortical neurons and the ontogeny of conditioned and unconditioned reflex control.

Suppression of an infantile reflex (circling behavior) to electric shock in a straight-alley escape problem increased as a function of age and trials in male Swiss-Webster mice trained at 7, 9, or 11 days of age and retested 24 h later. Twenty-four hours retention of prior training, indicated by the superior performance of trained subjects relative to yoked-shock and age controls, was not evident until 9 days of age. Analyses of Golgi--Cox preparations of parieto-temporo-preoccipital cortices, taken immediately following testing, revealed that behavioral development was paralleled by age-related changes in apical, oblique, and basilar dendritic networks and number of apical dendritic spines of layer V pyramidal cells. Correlations between behavioral and histological measures, indicated no consistent association of retention capacity with any of the physiological measures. However, basilar dendritic growth was significantly correlated with unconditioned reflex control as well as initial learning ability.

Age Factors↗
PubMed1979

Sensory neglect after lesions of substantia nigra or lateral hypothalamus: differential severity and recovery of function.

Sensory neglect was studied in cats after unilateral lesions of: lateral hypothalamus (LH); internal capsule (IC) adjacent to the LH; substantia nigra (SN) or the ventromedial hypothalamus (VMH). Special behavioral tests were employed to yield quantifiable data and also to exclude any confounding due to simple movement deficits. Lesions of SN or IC produced severe and enduring contralateral visual and somesthetic deficits and a facilitation of ipsilateral visual responsiveness. In contrast, LH lesions sparing the adjacent IC produced only weak and transient deficits and VMH lesions had no effects on sensory function. This suggests that lesions of the SN or its forebrain connections are important for producing sensory neglect and that sensory deficits after LH lesions are due to infringement on fibers of passage to or from the SN. Lesions which produced neglect often suppressed the amplitude of flash evoked responses in the ipsilateral caudate nucleus and visual and association cortex. However, these evoked potential effects were transient. There was no effect on the spontaneous EEG and this fails to support the hypothesis of a lack of hemispheric arousal in sensory neglect. The results are discussed in relation to nigrotectal projections and the process of attention. This lesion-behavior model is suggested for studies of recovery of function.

Animals↗
PubMed1980

Coordination and integration in the hindleg step cycle of the rat: kinematic synergies.

The kinematics of the hindleg step cycle of the rat in the vertical domain is composed of 7 synergies. Additionally, a global spatiotemporal principle ensures that each segment of the leg is never displaced backwards. The concepts of flexion and extension are inadequate for the description of step kinematics. As a limb segment changes its orientation, it does so in relation to the next serially connected limb segment or else in relation to gravitation. We call these two aspects of kinematics 'movements' and 'displacements' respectively, and describe segment kinematics in these terms. Of the 7 kinematic synergies, 5 involve a specific invariant interplay between 'movements' and 'displacements'. Together with the two additional parts they form the skeleton around which the step is organized. The flexible and regulatory nature of the step is obtained by the superposition of biasable properties on top of this skeleton. These include the durations, amplitudes, and initial and final positions of movements-displacements. The formalization of the step cycle kinematics represents explicitly intralimb coordination and integration. It also specifies the demand made upon the muscular and neural background organization that mediates the kinematics in a language which is appropriate for neurophysiological investigation.

Animals↗
PubMed1981

Regional distribution of functions in parietal association area 7 of the monkey.

The functions of cells in different parts of area 7 were studied in 5 hemispheres of three stumptail macaques (Macaca speciosa). Activity of groups of cells was recorded in non-anesthetized animals using course microelectrodes. Functional maps covering the exposed part of area 7 showed that purely visual and oculomotor responses occurred in area 7a (PG) whereas the skin was dominantly represented in area 7b (PF). Vision was also represented in 7b but here together with somatic mechanisms. Oculomotor discharges were concentrated in the medial part of area 7a, whereas motor action of the arm and hand extended across the medial part of area 7. Motor actions of the mouth were represented most laterally. A statistically significant somatotopic arrangement of the body surface was also observed: the face was represented most laterally and the body and legs most medially with large overlapping regions. In the posterior part of 7a a kinesthetic region was found with representation of joints and muscles. The combination of visual and cutaneous activation was common more laterally than the combination of visual and somatomotor activation. Laterally the visual representation ended at the border between area 7 and area 2 of S I at a locus in front of which the S I receptive fields were located inside the mouth. These results indicate that different functions are represented in different degrees in different parts of area 7. Therefore, one important determinant of the results obtained by various research groups is the area of recording within area 7.

Animals↗
PubMed1981

Properties of kinesthetic neurons in somatosensory cortex of awake monkeys.

(1) To study neural mechanisms used to encode kinesthetic information in somatosensory cortex of awake monkeys, we recorded from 227 single neurons responsive to joint movement or specific postures of the forelimb or hand (kinesthetic neurons). Unit responses were characterized quantitatively with respect to: (a) firing patterns; (b) responses to ramp changes in joint position and joint velocity; and (c) responses to sinusoidal joint movements. (2) Kinesthetic neurons were divided into 3 groups. Rapidly-adapting neurons (44%) responded only to joint movement, giving a burst of impulses proportional to velocity. They showed no tonic responses to limb posture. Two populations of tonically active neurons were observed: slowly-adapting neurons (43%) and postural neurons (13%). Both types increased their firing rates with increasing degrees of flexion or extension, showing maximum excitation at the extremes of joint position in the preferred direction. They were distinguished by their sensitivity to the velocity of movement, the size of the angle over which they respond, and the phase relation of their responses to sinusoidal joint movement. (3) The firing rates of kinesthetic neurons in S-I cortex are functions of both joint angle and joint velocity. The importance of each component varies in the 3 classes: velocity of movement is the most important determinant of firing rates of rapidly-adapting and slowly-adapting kinesthetic neurons, and joint angle predominates the responses of postural neurons.

Animals↗
PubMed1981

Multiple-joint neurons in somatosensory cortex of awake monkeys.

(1) In the somatosensory cortex of alert monkeys, 55 neurons were found which receive convergent information from two or more adjacent joints. Most of these multiple-joint neurons were excited by postures of the hand, particularly those involved in grasping. (2) Three basic types of joint interactions were observed. The simplest neurons (occlusion neurons) responded to postures of several different joints, but combination of the preferred postures produced no further increase in firing. The more complex cells showed summated responses to combined postures of adjacent joints, or subliminal facilitation between joints. The responses of both summation neurons and subliminal facilitation neurons were graded with joint angle, and there was an optimum or preferred position for both joints which gave the strongest response. (3) Multiple-joint neurons may provide a neuronal substrate for extracting postural information from several different populations of kinesthetic neurons. They therefore act as feature-detecting neurons, abstracting information about specific body postures.

Animals↗