Biomedical subjects

T Mergner

Publications and source records attributed to T Mergner.

At least 55 records · Page 3Linked to original sources

PubMed1996

Control of the body vertical by vestibular and proprioceptive inputs.

The study examines the influence of vestibular and leg proprioceptive cues on the maintenance of the body vertical in human stance. Vestibular body orientation cues were changed by applying bipolar currents to both mastoid bones (cosine-bell wave form of 3.3 s duration, 1 mA current intensity). Proprioceptive input was modified by vibrating the tibialis anterior muscle (at f = 90 Hz, step of 5 s duration and 1 mm amplitude). Furthermore, the vestibular stimulus was paired with the muscle vibration using three different temporal relationships between the stimuli. Body lean responses were analyzed in terms of sway trajectories of the center of foot pressure on the body support surface (horizontal plane). With the anode on the right mastoid, vestibular body lean response was essentially straight towards the right side, and with the anode on left mastoid towards the left side. Vibration of right tibialis anterior muscle induced an almost straight body lean forward and to the right. Upon combined stimulation, responses with complex trajectory resulted, which depended on the stimulus interval. These responses reflected a superposition of the individual vestibular and proprioceptive effects. The results show that the body vertical is under the continuous control of leg proprioceptive and vestibular inputs, which sum linearly. We present a concept according to which these inputs are used for establishing a reference system for the control of the body vertical.

Adult↗

PubMed1996

Detection thresholds for object motion and self-motion during vestibular and visuo-oculomotor stimulation.

We compared the detection threshold for object motion with that of self-motion in space in healthy human subjects. Stimuli consisted of horizontal rotations of subjects' body with a fixation spot kept in fixed alignment with their heads (vestibular stimulus), rotation of the fixation spot relative to the stationary subjects (visuo-oculomotor stimulus), and a combination thereof by applying rotations of subjects body relative to the stationary object (sinusoidal oscillations, 0.025-0.4 Hz). Two series of experiments were performed. 1) One group of subjects was instructed to attend to, and to indicate the occurrence of, either object or self-motion. 2) A second group was instructed not only to detect the occurrence of a perception, but also to quality it either as object motion or self-motion, depending on which modality dominated perceptually. With either instruction it was found that all three stimulus conditions could evoke both, either an object motion perception or a self-motion perception. The detection thresholds of both perceptions were essentially similar. Thresholds were highest with the vestibular stimulus, intermediate with the stimulus combination, and lowest with the visuo-oculomotor stimulus. The vestibular threshold depended on stimulus frequency, in that it decreased with increasing frequency. Thereby, it became similar to the visuo-oculomotor one, which was essentially constant across frequency. Probability of occurrence of the perceptions in the first experimental series was considerably higher than in the second series, suggesting an important role of attentional mechanisms. In the second series, percent frequency of occurrence of veridical perception (object motion with visuo-oculomotor stimulus, self-motion with stimulus combination) was at chance level (50%) at low stimulus frequency, but was augmented considerably at high frequency. We assume that the latter effect is brought about by a visual-vestibular conflict measure by which the visual stimulus (light spot) is qualified as representing either a moving object or a spatial reference for self-motion. While at suprathreshold stimulus intensities the conflict can determine perception magnitude, at threshold levels its influence is restricted mainly on the probability of occurrence of object and self-motion perception.

Adult↗

PubMed1996

Is perceived angular displacement the time integral of perceived angular velocity?

Estimates of rotational self-displacement and self-velocity have been used interchangeably in vestibular psycho-physics to characterize vestibular ego-motion perception. However, the assumption underlying this indiscriminate use has never been tested. The assumption holds that the two estimates are equivalent, with the displacement estimates reflecting the time integral of the signal underlying the velocity estimate. We tested this hypothesis by directly comparing displacement and velocity estimates. Two groups of healthy young subjects (2 x n = 15) were presented with the same vestibular stimuli (horizontal whole body rotations in the dark in the form of velocity steps of 5, 10, 20, and 40 degrees/s with 1, 2, 4, 8, and 16 s duration, yielding position ramps of 5, 10, 20, 40, 80, 160, and 320 degrees total displacement). The first subject group estimated peak velocity, and the second group estimated total displacement, both groups using a comparable psychophysical procedure (Stevens' magnitude estimation). The experimentally obtained velocity estimates were used to predict the displacement estimates. To this end, the velocity signal was assumed to decay exponentially from the reported peak value (reflecting the dynamics of peripheral and early central vestibular mechanisms) and was mathematically integrated. Predicted and measured displacement estimates were similar when a time constant of 20 s was assumed, which is in good agreement with earlier studies. We conclude that vestibular displacement estimates can, indeed, be considered equivalent to vestibular velocity estimates, at least for the stimulus parameters used.

Adult↗

PubMed1996

Abnormalities of ocular motility in myotonic dystrophy.

Are the oculomotor disturbances in myotonic dystrophy (MD), i.e. reduced smooth pursuit (SP) gain and reduced saccadic peak velocity (PV), of muscular or central origin? To answer this question the following two approaches were used. (i) The performance of SP was compared with the patient's ability to suppress the vestibulo-ocular reflex (VOR) visually (VOR suppression; VOR-S). In the latter task the SP system is involved, but the eyes hardly move within the orbits. A parallel impairment of SP and VOR-S would indicate a central dysfunction. (ii) Peak saccadic velocity was compared between two saccades performed to and fro in rapid succession. The intention was to measure any myotonic effect which might build up after the first saccade and slow down the second saccade. We studied 15 MD patients and 15 age-matched controls. Stimuli for slow eye responses consisted of sinusoidal horizontal rotations of the SP target and/or the vestibular rotation chair at frequencies between 0.1 and 0.8 Hz. Saccades were analysed in terms of PV. accuracy, duration and latency, comparing centripetal versus centrifugal saccades at short and long intersaccadic intervals (ISI; 400 ms and 900 ms, respectively). The SP gain was reduced in patients compared with the controls, the effect being most pronounced (32% less) at the highest stimulus frequency. Whereas VOR was normal in the patients, VOR-S was clearly impaired (50% worse at 0.8 Hz). Despite normal saccadic accuracy, peak saccadic velocity was significantly lower in the patient group (23% less for saccades of 12 degrees amplitude), similarly for centrifugal and centripetal saccades; all these differences were independent of the ISI. Latency was normal with centrifugal saccades, but was considerably increased with centripetal saccades at short ISI (67% longer compared with controls). The observation of a parallel degradation of SP and VOR-S in the patients is interpreted in terms of a central deficit in the SP pathways. Thus, it appears that slow eye movements were not impaired by muscle dystrophy and myotonia to a considerable degree in our patients. The increase in saccadic latency for centripetal saccades at the short ISI also reflects a central deficit. However, the observed slowing of saccades might have a myopathic or neural origin; a distinction was not possible at present. A myotonic origin of the saccade slowing seems unlikely, because the effect was independent of the presaccadic activation of the relaxing (antagonistic) eye muscle.

Adolescent↗

PubMed1996

Vascular risk factors and arteriosclerotic disease in idiopathic normal-pressure hydrocephalus of the elderly.

BACKGROUND AND PURPOSE: There is some evidence from previous studies that idiopathic normal-pressure hydrocephalus (NPH) of the elderly might be linked to vascular leukoencephalopathy. The purpose of this study was to examine the prevalence and impact of vascular risk factors and vascular diseases in idiopathic NPH compared with a control cohort. METHODS: The prevalence of arterial hypertension; diabetes mellitus; hypercholesterolemia; hyperlipidemia; smoking; obesity; and cardiac, cerebrovascular, and other arteriosclerotic diseases was assessed in 65 patients with idiopathic NPH. The findings were compared with those of 70 patients with comparable age distribution. To describe the differences of the prevalences of vascular risk factors, odds ratios were obtained by univariate and multivariate analyses. RESULTS: The univariate analysis revealed significant associations between idiopathic NPH and arterial hypertension (prevalence, 54 of 65 [83%]; control group, 25 of 70 [36%]; P < .001) and diabetes mellitus (prevalence, 31 of 63 [49%]; control group, 20 of 70 [29%]; P < .015) but not with other vascular risk factors. After multivariate regression analysis, only hypertension remained significantly associated with NPH (P < .0001). There was also a significant association between NPH and cardiac (P < .001), cerebral arteriosclerotic (P = .007), and other arteriosclerotic diseases (P = .001). A positive association was found between the severity of clinical symptoms of NPH and the presence of hypertension, especially for gait disturbance. The presence of hypertension was not related to the duration of NPH. CONCLUSIONS: Our data show a highly significant association between idiopathic NPH and arterial hypertension. Arterial hypertension might be involved in the pathophysiological mechanisms promoting idiopathic NPH.

Aged↗

PubMed1995

Combined action of optokinetic reflex (OKR) and vestibulo-ocular reflex (VOR) in macaque monkey during transient stimulation.

Interaction of vestibulo-ocular reflex (VOR) and optokinetic reflex (OKR) was studied in macaque monkeys by recording horizontal eye movements during transient rotations of their heads and/or an optokinetic pattern in space. At low peak velocities of the stimuli (1.25 degrees/s, 10.0 degrees/s) the eyes were rather well stabilized on the optokinetic pattern, independently of whether the head, the pattern, or both were rotated. At higher velocities (40.0 degrees/s), the OKR gain was attenuated and, when combining vestibular and optokinetic stimuli, the eyes became increasingly stabilized in space. The data could be simulated by a computer model previously designed to describe VOR-OKR interaction during sinusoidal rotations. In this model eye stabilization primarily relies on the OKR, while the role of the VOR is to compensate for the limited bandwidth of the OKR.

Animals↗

PubMed1995

Eye stabilization by vestibulo-ocular reflex (VOR) and optokinetic reflex (OKR) in macaque monkey: which helps which?

VOR-OKR interaction was studied in macaque monkey in the frequency domain, using various vestibular-visual stimulus combinations in the horizontal plane. At low stimulus frequencies (< 0.1 Hz), the eyes were always stabilized on the optokinetic pattern, irrespective of whether the head, the pattern, or both were rotated. At higher frequencies, the gain of the OKR attenuated, and concomitantly the eyes became increasingly stabilized in space. These findings show that the VOR becomes functionally relevant only at high frequencies. It compensates for the limited bandwidth of the OKR, thereby improving vision provided the pattern to be fixated is stationary in space.

Animals↗

PubMed1995

Visual short-term memory of stimulus velocity in patients with unilateral posterior brain damage.

Neurophysiological studies indicate the existence of an area in the extrastriate monkey cortex specialized for the processing of stimulus motion. The present investigation was conducted to determine whether a homologous area exits in the human cortex that underlies the processing and short-term storage of velocity information. Contrast detection and velocity discrimination thresholds were measured in a group of 23 patients with unilateral focal damage to either the lateral occipital, temporal, or posterior parietal cortex. Their results were compared to those of 23 age-matched control subjects. Detection and discrimination thresholds were determined for spatially truncated sinewave gratings presented 4 degrees eccentric of fixation randomly in either the left and right visual fields. Contrast detection thresholds were measured in a spatial two-alternative forced-choice paradigm for three different drift rates (1, 2, and 4 Hz) for leftward and rightward drift directions. Simultaneous velocity discrimination thresholds were determined for reference and test gratings presented 4 degrees left and right of fixation. Sequential velocity discrimination thresholds were measured using a delay, with a interstimulus interval (ISIs) of 1, 3, and 10 sec. In a subset of five patients with superior temporal lobe damage, spatial frequency discrimination thresholds for stationary gratings were also determined. The results indicate the following: (1) contrast detection thresholds for drifting gratings did not significantly differ between the patient and control groups; (2) velocity discrimination thresholds were significantly elevated in the patients; (3) velocity discrimination thresholds significantly increased with increasing ISI in the patients; (4) velocity discrimination thresholds were elevated most when the patients had a lesion in the superior temporal cortex; (5) in the subgroup of five patients with superior temporal lobe damage, spatial frequency discrimination thresholds were not significantly elevated. The results suggest that there is a visual area in the human posterior temporal cortex that is involved in the processing and short-term storage of the velocity of moving visual stimuli.

Adolescent↗

PubMed1993

Perception of horizontal head and trunk rotation: modification of neck input following loss of vestibular function.

Chronic loss of vestibular function modifies the role of neck afferents in human perception of self-motion. We characterized this change by comparing the self-motion perception of patients with chronic vestibular loss (Ps) to that of normal subjects (Ns). Stimuli consisted of sinusoidal horizontal rotations (0.025-0.4 Hz) of the trunk relative to the head (neck stimulation) and/or of the head in space (vestibular stimulation). Perception of head rotation relative to the trunk, of trunk rotation in space, or of head rotation in space was assessed in terms of gain and phase (veridical perception, G = 1 and phi = 0 degree) as well as detection threshold using a pointing procedure. (1) Perception of head rotation relative to the trunk (neck proprioception). Ps' detection threshold of head-to-trunk rotation was normal (i.e. similar to that of Ns) across all frequencies tested. Also, with peak angular velocities above 5 degrees/s, the gain of their perception was approximately normal. When peak velocity was decreased below this value, however, either by lowering stimulus frequency with peak displacement kept constant (+/- 8 degrees) or by decreasing peak displacement at constant frequency (0.05 Hz), the gain increased above unity, unlike in Ns. In contrast, the phase remained normal (approximately 0 degree). (2) Perception of trunk rotation in space. Ps perceived their trunks as stationary during neck stimulation and all vestibular-neck combinations at medium to low frequencies. At 0.4 Hz, however, Ps consistently perceived the trunk rotation, conceivably due to somatosensory self-motion cues arising from high body acceleration. In contrast, Ns perceive a trunk-in-space rotation with the neck stimulation and most of the stimulus combinations across the whole frequency range tested. Ns perceived their trunks as stationary only during head rotation on the stationary trunk (presumed to reflect a mutual cancellation of neck and vestibular signals). (3) Perception of head rotation in space. In Ps, unlike Ns, this perception always resembled that of head rotation relative to the trunk. (4) When Ps were presented with a visual or somatosensory space reference (not motion cues), their perception of trunk and head rotation in space became approximately normal. (5) We suggest that there are basically two changes in the neck-induced self-motion perception associated with chronic vestibular loss. First, neck proprioception shows a non-linear gain that overemphasizes low stimulus velocities, for unknown reasons.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗

PubMed1993

Interaction of vestibular and proprioceptive inputs.

The study investigates the interaction of leg proprioceptive and vestibular afferents for human self-motion perception in space. Stimulation consisted of sinusoidal (0.025-0.4 Hz) and transient horizontal rotations of trunk and head in space (vestibular stimulus, VEST) and of the feet relative to the trunk (leg proprioceptive stimulus, LEG-PROP). Measures of the perception were obtained with the help of a pointing procedure. Leg proprioception. The perception of relative motion between feet and trunk during LEG-PROP was veridical across the frequencies tested and had a low detection threshold (0.2 degree/s). Perception of trunk turning in space. Trunk turning during VEST was underestimated, especially at low frequencies, and the threshold of the perception was > or = 1.0 degree/s. LEG PROP evoked an illusion of trunk turning, which reached a considerable magnitude at low frequencies. During VEST-LEG-PROP combinations, the perception varied monotonously as a function of both inputs. Reflecting the deficiencies of its constituents, it was erroneous with 1 exception. During trunk rotation about the stationary feet, the perception was approximately veridical across frequency and its threshold was down to 0.2 degree/s, suggesting that it was determined essentially by leg proprioception in this condition. These findings resemble those previously obtained for neck proprioception and, therefore, were incorporated into a conceptual model of vestibular-proprioceptive interaction in general. In this model, first an internal notion of foot in space is created by summing the following high-threshold signals: head in space (vestibular), trunk relative to head (neck proprioceptive), and foot relative to trunk (leg proprioceptive). Second, further addition of low-threshold proprioceptive signals of trunk on foot and head on trunk yields the perception of trunk in space and head in space, respectively. Not included in the model is the finding that subjects' perceptual mode may change in certain conditions. When foot excursion exceeds a certain magnitude, for instance, vestibular input alone may determine the self-motion perception.

Adult↗

PubMed1993

Delayed pattern discrimination in patients with unilateral temporal lobe damage.

Behavioral and neurophysiological studies in macaque monkeys suggest a role of the inferior temporal cortex in pattern discrimination and visual memory. To determine whether this cortical area is also involved in human short-term visual memory, we measured spatial frequency discrimination thresholds for sequentially presented stimuli in 17 patients with unilateral, postoperative focal damage to the temporal cortex (11 left, 6 right hemisphere). These results are compared to those of 17 age-matched control subjects. Contrast detection thresholds and difference thresholds for spatial frequency were determined for spatially truncated sine wave gratings presented in the left and right visual fields. Detection thresholds were measured for sine wave gratings in a spatial two-alternative forced-choice procedure for three spatial frequencies [2.5, 5, and 10 cycles (c)/degree] for each hemifield. Discrimination thresholds were determined for two gratings sequentially presented either 4 degrees to the left or right of fixation. Grating contrast was five times the value of detection threshold and reference frequency was 5 c/degree. Within each trial, the gratings were separated in time by 1, 3, and 10 sec interstimulus intervals (ISIs), and subjects signaled which grating had the higher spatial frequency. The results indicate that (1) contrast detection thresholds overall did not differ between patient and control groups; (2) spatial frequency discrimination thresholds were, however, significantly elevated in patients and this elevation was significantly more pronounced in the visual field contralateral to the damaged hemisphere; and (3) patients with inferotemporal damage exhibited higher discrimination thresholds for the longest ISI, whereas patients with medial/superior temporal lobe damage did not show this effect. The results suggest that visual areas in human temporal cortex are involved in the higher visual processes underlying delayed pattern discrimination.

Adult↗

PubMed1992

Interaction of vestibular and proprioceptive inputs for human self-motion perception.

Human perception of horizontal self(body)-motion in space was studied during various combinations of vestibular and leg-proprioceptive stimuli in the dark. During sinusoidal rotations of the trunk relative to the stationary feet (functionally synergistic combination) the perception was almost veridical over the frequency range tested (0.025-0.4 Hz). This finding suggested a dominance of the proprioceptive over the vestibular input, since the quantitative aspects of the perception (gain, phase, and detection threshold): (a) closely resembled those of the proprioceptive foot-to-trunk perception, and (b) clearly differed from those of the vestibular self-motion perception. However, when using other combinations, the self-motion perception changed in a monotonous way as a function of the two inputs, indicating that the two inputs do interact in a linear way. In a model of these findings the interaction occurs in two stages: (1) summation of a vestibular trunk-in-space signal and a (dynamically matched) proprioceptive foot-to-trunk signal yields an internal representation of foot support motion in space; (2) superposition of the latter by an almost ideal proprioceptive trunk-to-foot signal results in a representation of trunk-in-space motion (essentially proprioception-dependent and ideal when the feet are stationary).

Foot↗

PubMed1992

Role of vestibular and neck inputs for the perception of object motion in space.

UNLABELLED: The contribution of vestibular and neck inputs to the perception of visual object motion in space was studied in the absence of a visual background (in the dark) in normal human subjects (Ss). Measures of these contributions were obtained by means of a closed loop nulling procedure; Ss fixed their eyes on a luminous spot (object) and nulled its actual or apparent motion in space during head rotation in space (vestibular stimulus) and/or trunk rotation relative to the head (neck stimulus) with the help of a joystick. Vestibular and neck contributions were expressed in terms of gain and phase with respect to the visuo-oculomotor/joystick feedback loop which was assumed to have almost ideal transfer characteristics. The stimuli were applied as sinusoidal rotations in the horizontal plane (f = 0.025-0.8 Hz; peak angular displacements, 1-16 degrees). RESULTS: (1) During vestibular stimulation, Ss perceived the object, when kept in fixed alignment with the moving body, as moving in space. However, they underestimated the object motion; the gain was only about 0.7 at 0.2-0.8 Hz and clearly decreased at lower stimulus frequencies, while the phase exhibited a small lead. (2) During pure neck stimulation (trunk rotating relative to the stationary head), the object, when stationary, appeared to move in space counter to the trunk excursion. This neck-contingent object motion illusion was small at 0.2-0.8 Hz, but increased considerably with decreasing frequency, while its phase developed a small lag. (3) Vestibular, neck, and visuo-oculomotor effects summed linearly during combined stimulations. (4) The erroneous vestibular and neck contributions to the object motion perception were complementary to each other, and the perception became about veridical (G approximately 1, phi approximately 0 degree), when both inputs were combined during head rotation with the trunk stationary. The results are simulated by an extended version of a computer model that previously had been developed to describe vestibular and neck effects on human perception of head motion in space. In the model, the perception of object motion in space is derived from the superposition of three signals, representing "object to head" (visuo-oculomotor; head coordinates), "head on trunk" (neck; trunk coordinates), and "trunk in space" (vestibular-neck interaction; space coordinates).

Humans↗

PubMed1992

Dependence of presaccadic cortical potentials on the type of saccadic eye movement.

Premovement cortical potentials were studied with 4 types of saccadic eye movement: (a) visually triggered saccades of normal reaction time (RT; regular saccades); (b) visually triggered saccades of extremely short RT (express saccades); (c) saccades towards predicted target locations (anticipatory saccades); (d) saccades back towards predicted location of fixation point (refixation saccades). With all 4 saccade types a "presaccadic negativity" with the maximum at the vertex (Cz) was observed. A bilaterally symmetrical component contained in this potential (being smallest with almost unconsciously performed refixation saccades and smaller in trained than in naive subjects) appeared to be related mainly to the subjects' volitional effort. In addition, anticipatory and refixation saccades were preceded by an early, widespread contralateral negativity, which we relate to cortical activities that prepare, in general terms, action within or towards the hemifield containing the saccade goal. During the 60 msec before anticipatory saccades, a negativity occurred over the contralateral central lead, which may reflect neural activation in the frontal eye field (FEF) and premotor cortex. In contrast, regular saccades were preceded 30 msec before onset by a negativity over the contralateral parietal cortex, which probably reflects an activation of parietal visuo-motor neurons. No lateralization of the cortical potentials was observed before express saccades, which suggests that these saccades are generated in a reflex-like way mainly by subcortical mechanisms.

Adult↗

PubMed1992

[Neurologic complications of Q-fever (Coxiella burnetii)].

We report on fifteen patients with a typical syndrome of Q-fever. Four patients (= 27%) showed signs of nervous system involvement. One patient developed a meningitic syndrome, another patient had a passing psychosis. In two patients, severe cerebellar deficits were predominant. It is pointed out that these two patients were under lithium therapy because of manic-depressive illness. A synergetic neurotoxic effect of cociella burneti infection and lithium is discussed as a possible cause of the severe cerebellar pattern of symptoms.

Adult↗

PubMed1992

Saccadic reaction times in patients with frontal and parietal lesions.

The effect of unilateral circumscribed lesions in different areas of the frontal and parietal cortex on the distributions of saccadic reaction times (SRTs) was investigated in 32 patients under four stimulus conditions: (i) gap-random: a target light appeared 200 ms after extinction of a central fixation light randomly at 8 degrees either left or right; (ii) overlap-random: like (i), but the fixation light remained on ('overlap'); (iii) gap-simultaneous: two peripheral lights appeared simultaneously left and right 200 ms after the extinction of the fixation light, one predesignated by instruction as saccadic target; (iv) overlap-simultaneous: like (iii), but the fixation light remained on. Depending on SRT and condition and based on the data of control subjects, we evaluated the percentages of anticipatory (SRT: 0-90 ms), express (91-157 ms) and regular (158-400 ms) saccades, of time (> 400 ms) and direction errors as well as the mean latencies and the standard deviations. These data were compared across control subjects, frontal lobe patients with a lesion in the region of the frontal eye field (FEF), and frontal patients with a lesion outside the FEF, as well as across control subjects, parietal lobe patients with a lesion in the dorsolateral region, and parietal patients with a lesion outside the dorsolateral region. (i) Frontal patients with a lesion in the FEF region showed an increased percentage of express saccades (gap-random condition), especially with saccades directed towards the side of the lesion (ipsilateral). If fixation was not interrupted prior to target appearance (overlap-random), express saccades were largely suppressed, similar to normals. All patients with a frontal lesion, whether in the region of the FEF or not, showed a decreased percentage of contralateral anticipatory saccades (gap-simultaneous), whereas the percentages of direction and time errors were in the normal range, even if more than one stimulus was presented (e.g. overlap-simultaneous condition). (ii) Patients with dorsolateral parietal lesions showed decomposed SRT patterns (high SRT variability, increased percentages of time and direction errors, decreased percentages of express and anticipatory saccades). The decomposition had a contralateral preponderance and increased if more than one stimulus was visible beside the saccadic target. Our results suggest that FEF lesions impair mainly the volitional control over visually triggered express or reflex-like saccades if fixation is disrupted, whereas dorsolateral parietal lesions impair mainly the selection of the visual targets.

Adult↗

PubMed1991

Human perception of horizontal trunk and head rotation in space during vestibular and neck stimulation.

The vestibular signal of head motion in space must be complemented by a neck signal of the trunk-to-head excursion in order to provide the individual with information on trunk motion in space. This consideration led us to study psychophysically the role of vestibular-neck interaction for human self-motion perception. Subjects (Ss) were presented with passive horizontal rotations of their trunk and/or head (sinusoidal rotations, f = 0.025 - 0.4 Hz) in the dark for vestibular and neck stimulation, as well as for combinations of both. Ss' perception was evaluated in terms of gain (veridical perception of stimulus magnitude, G = 1), phase, and detection threshold. (1) Perception of trunk rotation in space. During vestibular stimulation (whole-body rotation) and neck stimulation (trunk rotation with the head kept stationary) the frequency-transfer characteristics underlying this perception were very similar. The gain fell short; it was only about 0.7 at 0.4 and 0.2 Hz stimulus frequency and was further attenuated with decreasing frequency. In contrast, the phase was close to that of actual trunk position. The gain attenuation was found to be a function of the peak angular velocity of the stimulus, a fact, which we related to a 'velocity threshold' of the order of 1 deg/s. During the various vestibular-neck combinations used, Ss' perception was again erroneous, reflecting essentially the sum of its two non-ideal constituents. However, there was one noticeable exception; during the combination 'head rotation on stationary trunk', Ss veridically perceived their trunk as stationary (compatible with the notion that the sum yielded 'zero'). (2) Perception of head rotation in space. During vestibular stimulation, Ss' estimates showed the same non-ideal gain-vs.-frequency characteristics as described above for the trunk. Neck stimulation induced an illusion as if the head had been rotated in space. This neck contribution was such that, when it was combined with its vestibular counterpart during head rotation on stationary trunk, the perception became almost veridical. On closer inspection, however, this neck contribution was found to reflect the sum of two components; one was the non-ideal neck signal contributing to the perception of 'trunk in space', the other was an almost ideal neck signal of head-on-trunk rotation. (3) The results could be described by a simple model. In this model, the erroneous vestibular signal 'head in space' is primarily used to create an internal representation of 'trunk in space'.(ABSTRACT TRUNCATED AT 400 WORDS)

Head↗

PubMed1991

Sensitivity of external cuneate neurons to neck rotation in three-dimensional space.

A functionally meaningful vestibular-neck interaction, such as it has been demonstrated for postural reflexes and self-motion perception, requires the spatial and temporal response characteristics of vestibular and neck signals to be similar. We investigated the spatial coding in neurons of the external cuneate nucleus (ECN) with natural neck and vestibular stimulations, and compared them to that of neurons in the descending and medial vestibular nuclei (DVN and MVN, respectively) obtained with vestibular stimulation. Neurons were recorded extracellularly in chronically prepared cats held under light barbiturate anesthesia. Neck stimulation was performed by sinusoidally rotating the animals' trunk relative to the earth-fixed head in six different vertical planes and in the horizontal plane. Vestibular stimulation was elicited by whole-body rotations in the corresponding planes. During neck stimulation in the vertical planes, most ECN neurons showed an approximately sinusoidal discharge modulation about resting rate, which became maximal during rotation in a specific plane. Off this plane, the response declined along a cosine function and reached zero in the orthogonal plane. The majority of these ECN neurons also responded to horizontal neck rotation; the resulting "optimal" direction of rotation in three-dimensional space varied considerably among the neurons. Yet, there was a certain preference; the majority of these ECN neurons fired maximally if trunk rotation in the yaw plane stretched the neck on the ipsilateral side, if roll brought the contralateral shoulder closer to the head, and if pitch brought the back closer to the occiput. A minority of ECN neurons showed more complex response patterns which could not be described by a single, optimal direction. About one third of the neck-sensitive ECN neurons tested showed weak responses during whole body rotation, which might stem from a weak vestibular input to this nucleus. In the DVN and MVN, the optimal direction in three-dimensional space with vestibular stimulation typically had a cosine-like spatial tuning. The spatial distribution of these directions clearly differed from that of neck-sensitive neurons in the ECN. We therefore assume that a further processing of the two input signals takes place at later stages in the CNS (e.g., in the vestibulo-cerebellum) in order to yield a functionally useful vestibular-neck interaction.

Animals↗