The activity of axons located mainly in the ventral part of the lateral funiculi of the cervical segments C2-C3 were recorded in precollicular decerebrate cats and their responses to lateral tilt of the whole animal studied. Units were identified according to their antidromic and/or transynaptic responses to stimulation of the ipsilateral lateral reticular nucleus (NRL) as well as their responses to ipsilateral and/or contralateral forelimb nerve stimulation. In most respects, those units which could be antidromically identified as cervical ascending tract axons showed properties similar to those described for neurons of the spinoreticular pathway, the bVFRT. Among the 106 recorded units, 42 responded to 15 degrees tilts in the median plane. Steady changes in unit discharge frequency were evoked by tilting, which lasted as long as the position of the cat was maintained. The response of the units to tilting consisted of increased in discharge rate during tilt in one direction, while tilt in the opposite direction resulted in a decrease in discharge rate. The magnitude of the responses was clearly related to the degree of tilt. All the units affected by tilt, except one, received inputs from both ipsilateral and contralateral forelimb nerves and some of them also from high-threshold neck muscle afferents. Furthermore, 12 of these units could be orthodromically excited at short latency from the ipsilateral brain stem, suggesting a possible monosynaptic input perhaps transmitted via the lateral vestibulospinal tract. The responses of the cervical ascending spinal tract units to tilt did not appear to depend on peripheral proprioceptive or cutaneous feedback since a number of precautions were taken to eliminate such influences, while control experiments in animals submitted to partial or complete bilateral VIIth nerve section showed the number of neurons responsive to tilt to be profoundly reduced or eliminated. It appeared also that the average spontaneous discharge rate of the ascending units was much lower following bilateral VIIth nerve section than that obtained from the corresponding units recorded in preparations with the VIIth nerves intact. These findings suggested that the responses of the cervical ascending neurons to tilt as well as their spontaneous background activity depended on influences arising from the macular labyrinthine receptors. The observation that the responses of these ascending neurons to peripheral nerve stimulation are modified by tilt further suggested that the macular system may interact with the somatosensory system originating from the forelimb and the neck musculature, thus being able to produce the fine adjustments that cerebellar and brain stem structures exert in the control of posture and movements.

Animals↗

PubMed1976

Temporal distribution of rapid eye movements and related monophasic potentials in the brain stem following injection of an anticholinesterase.

The temporal distribution of the horizontal rapid eye movements and the related monophasic potentials recorded from the ascending MLF following intravenous injection of o.i mg/kg of anticholinesterase has been investigated in precollicular decerebrate animals. In particular the intervals between individual MLF potentials occurring during successive REM episodes have been evaluated over a total period of 2000 sec on each experiment. 2. There was a bimodal distribution of intervals due to the fact that all the rapid eye movements and the related MLF potentials were grouped in bursts which occurred at quite regular intervals. 3. During the cholinergically induced episodes of REM, there were usually bursts of REM in one direction followed by bursts of REM in the opposite direction. The mean number of individual eye movements within each burst was 4.67 +/- 0.84, S.D., while the average interval between the individual eye movements corresponded to 167 +/- 36 msec, S.D. 4. There was a great regularity in the periodic occurrence of the bursts of REM. In particular the mean interval between the beginning of a burst of REM in one direction (i.e., towards the left side) and that of the next train oriented in the opposite direction (i.e., towards the right side) was 1.97 +/- 0.47 sec, S.D., while the mean interval between the beginning of this last train and that of the successive train oriented in the former direction corresponded to 2.97 +/- 0.48 sec, S.D. Moreover, the duration of the whole period corresponding to the interval between two successive bursts of REM oriented in the same direction (i.e., towards left or towards right) corresponded on average to 4.94 +/- 0.55 sec S.D. and 4.99 +/- 0.52 sec, S.D. respectively. 5. In addition to these "simple bursts" of rapid eye movements oriented in one direction, there were "complex bursts" in which an alternation of the individual eye movements within each burst was observed. In these instances the mean number of spikes was greater (5.35 +/- 1.20, S.D.) and the mean interval shorter 119 +/- 44 msec, S.D.) than those observed in the "simple bursts", About 10-15% of the bursts occurring during the cholinergically induced REM episodes were of the complex type. 6. These findings obtained from an individual experiment were confirmed in all the decerebrate animals treated with the same dose of anticholinesterase; only slight quantitative differences were detected from case to case. 7. Since the bursts of REM induced by the anticholinesterase depend upon the activity of the vestibular nuclei, it is postulated that cholinergic reticular neurons activate structures which show waxing and waning in their activity before acting on the vestibulo-oculomotor system. This system probably contains the inhibitory interneurons which transform the regularly modulated input into a rhythmic vestibular output...

Animals↗

PubMed1976

The oscillatory system responsible for the oculomotor activity during the bursts of REM.

1. In precollicular decerebrate cats the electrical activity of single pontine neurons was recorded before, during and after the episodes of postural atonia produced by i.v. injection of 0.03-0.1 mg/kg of eserine sulphate. These episodes were characterized by the regular occurrence of horizontal conjugate eye movements, which were mainly grouped in bursts of REM; moreover, a burst of REM in one direction was generally followed by a burst of REM in the opposite direction. 2. Among the recorded units, 32 showed an increase in their discharge rate during these cataplectic episodes. However, while these units fired at regular frequency when postural rigidity was present, they showed periodic changes in their discharge rate as soon as the bursts of REM appeared in the electrooculogram. In particular a nearly sinusoidal increase in the discharge rate was related to the appearance of an ocular burst in one direction, while a decrease in the unit discharge occurred during an ocular burst in the opposite direction. In some instances neighbouring pontine units located within each side of the brain stem showed reciprocal rate profiles during REM bursts oriented in a given direction, making it likely that the cyclic alternation of their activity depended upon their reciprocal interaction. 3. The alternative hypothesis, i.e., that these periodic changes in unit discharge depend upon the proprioceptive feedback due to the eye movements was excluded by the fact that these changes started before the occurrence of the bursts of REM and began to decline before the end of the burst. Moreover no variation in their firing rate was observed during the positional nystagmus induced by tilting the animal in the control period, i.e., when postural rigidity had reappeared following the end of the cataplectic episode. 4. Most of the neurons showing periodic changes in their discharge frequency during the bursts of REM were located in the pontine reticular formation. Scattered units were also found within the region of the locus coeruleus and the raphe system, close to the surrounding reticular structures. 5. In addition to these neurons, 60 pontine units were recorded, which did not show any changes in their discharge rate during transition from the control period to the cataplectic episode. However, phsiic increases or phasic decreases in their discharge rate appeared synchronously with the individual eye movements. Since in most instances these phasic changes in unit activity coincided with the appearance of the individual monophasic potentials recorded from the ascending MLB, which immediately preceded the rapid eye movements, these units could be attributed either to the premotor neurons responsible for these REM or to the closely related structures which generate their rhythmic discharge. In only a few instances did the discharge of these units not precede but follow the individual eye movements, indicating that they resulted from a proprioceptive feedback originating during the eye movements. 6...

Animals↗

PubMed1974

Macular influences on ascending spinoreticular neurons located in the cervical cord.

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Animals↗

PubMedDate not supplied

Visual discrimination and short-term memory for random patterns in patients with a focal cortical lesion.

Visual discrimination and short-term recognition memory for computer-generated random patterns were explored in 23 patients with a postsurgical lesion in one of the cortical hemispheres. Their results are compared with those of 23 age-matched volunteers. In a same-different forced-choice discrimination task, d' and log beta (measures of sensitivity and bias), as well as reaction time (RT) were determined. All participants viewed patterns defined either by luminance contrast or isoluminant red-green color contrast, the amplitude of which was adjusted to be 10 times the respective detection threshold level. Block patterns consisting of a 6 x 6 matrix of light and dark (red and green) checks were randomly configured on each presentation. They were presented in pairs, randomly in two visual quadrants for a duration of 200 msec. Three presentation conditions were used: simultaneous presentation of reference and test stimulus, sequential presentation with a short delay (interstimulus interval, ISI = 3 s), and sequential presentation with a long delay (ISI = 6 s). The results indicate that patients with a lesion in the occipitotemporal cortex, the superior temporal cortex and the frontal cortex were significantly impaired on both luminance-contrast and color-contrast pattern discrimination. Patients with damage in the anterior inferotemporal cortex showed no overall impairment. The results suggest that performance in visual discrimination and recognition memory tasks rely on distributed neural processes with more than one neocortical location.

Adult↗

PubMedDate not supplied

Perception of horizontal head and trunk rotation in patients with loss of vestibular functions.

In patients with loss of vestibular functions, we studied psychophysically the self-motion perception for 'trunk in space' and 'head in space' during various combinations of horizontal head and trunk rotation in the dark. The results were compared to those of normal subjects. For their 'trunk in space' perception, the subjects relied on their internal image of space, derived from the vestibular receptors in the head, and referred their trunk to this as a reference by adding to it a nuchal trunk-to-head signal. The patients, by contrast, always considered the trunk as stationary. Obviously because they were devoid of any space cues, they abandoned or suppressed a neck contribution to their 'trunk in space' perception, which, in fact, would yield an erroneous perception in almost all conditions in the dark. Both the patients and the subjects based their 'head in space' perception on their internal representation of 'trunk in space' and added to this a nuchal head-to-trunk signal. However, the patients' head-to-trunk signal, unlike that of the subjects, was considerably larger than the actual head-to-trunk rotation at low stimulus frequency. We relate this finding to some unconscious modification of their neck muscle activity during passive head rotation. It appears that the patients' gain of the neck input per se is not increased, but rather that subsets of this input are modified according to the particular function they serve.

Adolescent↗

PubMedDate not supplied

Visual object localization through vestibular and neck inputs. 1: Localization with respect to space and relative to the head and trunk mid-sagittal planes.

Object localization in space signals in the absence of an external reference (visual, auditory, haptic) involves a signal of the head in space (vestibular). The present study asks whether signals of body position relative to the support surface (proprioceptive) are involved as well, by investigating the role of vestibular-neck interaction (dissociating head and trunk position). Normal human subjects saw a light spot (object) and continuously nulled displacement steps of the spot. They did so before and after vestibular and/or neck rotational stimulation in the horizontal plane, reproducing a predesignated object localization in space (i), relative to the head mid-sagittal (ii), and relative to the trunk mid-sagittal (iii). The predominant frequency contained in the stimuli was varied (0.05, 0.1, and 0.4 Hz). (I) Object localization in space upon whole-body rotation (vestibular stimulus) at high frequency was veridical, whereas that at low frequency fell short. Almost identical results were obtained for trunk rotation about the stationary head (neck stimulus). In contrast, when combining the stimuli in the form of head rotation on the stationary trunk, the results were veridical, independent of stimulus frequency. Additional findings obtained with a large variety of vestibular-neck stimulus combinations suggest a linear summation of vestibular and neck signals. (II) Object localization with respect to the head was approximately veridical, being independent of vestibular and neck stimulation. However, this only applied if subjects were not biased by a head-in-space motion illusion of neck origin. (III) Object localization with respect to the trunk was veridical in all conditions tested. The findings support a recently developed concept, according to which humans evaluate the kinematic state of a visual object in space by (a) relating it to that of the body support by means of an essentially ideal proprioceptive coordinate transformation, and (b) relating, in turn, the kinematic state of the support to a vestibularly derived notion of space, using a proprioceptive coordinate transformation that "knows" the vestibular transfer characteristics. One important aspect is that object localization in space always is veridical during head and trunk rotation relative to a stationary support (for example, the ground) despite non-ideal vestibular transfer characteristics. Additional findings in patients with chronic loss of vestibular function confirm this concept.

Adult↗

PubMedDate not supplied

Vestibular-neck interaction and transformation of sensory coordinates.

The article considers findings and concepts on vestibular-proprioceptive interaction for self-motion perception and postural control under the form of simple describing models. It points out that vestibular-neck interaction is only a small fraction of an extended mechanism of co-ordinate transformations. This links together the different parts of our bodies, so that sensory information arising in one part of the body can be used for perceptual or motor tasks in other parts. Particular emphasis is put on the problems that arise from imperfect signal transduction in the vestibular semicircular canal systems at low stimulus frequencies/velocities. Also, a "down-and-up-channeling" principle is suggested, by which the body support is linked via coordinate transformations to the internal notion of physical space provided by the vestibular system. Furthermore, the following question is addressed: how does the brain use visual input to overcome the vestibular deficiencies, at the risk of visual self-motion illusions? Finally, a conceptual model of postural control is presented in which a proprioceptive feedback loop that links the body to its support surface is merged with a loop for postural stabilization in space.

Humans↗