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PubMed2006

Visually induced postural sway in anxiety disorders.

Postural sensitivity to moving visual environments in patients with anxiety disorders was studied. We hypothesized that patients with anxiety disorders would have greater sway in response to a moving visual environment compared to healthy adults, especially if they have space and motion discomfort (SMD). Twenty-one patients with generalized anxiety without panic (NPA) and 38 patients with panic and agoraphobia (PAG) were compared to 22 healthy controls. SMD was evaluated in all subjects via questionnaire. Subjects stood on a force platform that was either fixed or rotating with the subject (i.e., sway referenced) during exposure to a sinusoidally moving visual surround. Center of pressure (COP) data were computed from force transducers in the platform as a measure of sway. Results showed that patients swayed significantly more in response to the moving visual scene compared to control subjects, with no differences between the NPA and PAG groups. SMD was a predictor of sway response in the patients: patients with high SMD swayed significantly more than both Controls and anxiety patients with low SMD. These results indicate that patients with anxiety disorders, particularly those with SMD, are more visually dependent for balance. This subgroup of patients may be amenable to treatment used for patients with balance disorders (i.e., vestibular rehabilitation) that focuses on sensory re-integration processes that address visual sensitivity.

Adolescent↗
PubMed2000

Vestibular perception of self-rotation in different postures: a comparison between sitting and standing subjects.

We investigated whether posture - either seated (S) or upright standing (O, orthostatic) - affects the vestibular perceptions of angular velocity (V) and displacement (D) in the horizontal plane. We also examined whether the two perceptions are equivalent, that is, whether perceived displacement can be viewed as the time integral of perceived velocity. Sinusoidal stimuli were delivered to subjects sitting on a Barany chair or standing on a turning platform. Frequencies ranged from 0.028 Hz to 0.45 Hz, peak-to-peak amplitudes from 11.3 degrees to 180 degrees, and peak velocities from 4 degrees/s to 64 degrees/s. Perceptions were measured by retrospective magnitude estimation in relation to a standard stimulus (STD) of 0.11 Hz, 45 degrees, 16 degrees/s. For D-estimates, two different moduli were assigned to the STD: Either "45 degrees" (allowing subjects to use the familiar degree scale, which can easily be related to the body scheme) or "10" (which bears no relation to an accustomed scale). For V-estimations the modulus was always "10" (there is no "natural" velocity scale). D-estimates exhibited only a marginal, non-significant dependence on posture (S larger than O); they were highly veridical (linear function of stimulus amplitude, gain close to 1) when subjects used the degree scale but had a reduced gain (approximately 0.76) with a modulus of 10. V-estimates, on the other hand, varied with posture (S significantly larger than O), particularly upon presentation of large stimuli; also, they deviated increasingly from veracity as stimulus magnitude increased (saturating function). Finally, posture had no effect upon the vestibular detection threshold. The frequency response of D-estimates, tested with stimuli of constant amplitude and varying frequency, was bimodal at low frequencies: stimuli were either not detected at all or were veridically estimated, on average (with a large scatter, though). The frequency response of V-estimates, tested with stimuli of constant peak velocity, exhibited a continuous increase with stimulation frequency. We conclude that published quantifications of vestibular self-motion perception, collected mostly with sitting subjects, are likely to be applicable also to the more natural situation of standing subjects provided they are based on displacement indications; in contrast, velocity indications appear to be modulated by posture. The different susceptibility of displacement and velocity estimates to posture and their incongruent frequency characteristics suggest that perceived displacement does not, or does not always, equal the time integral of perceived velocity. The persistence of nearly veridical displacement estimates at low frequencies suggests the intervention of cognitive processes.

Acceleration↗
PubMed1996

Perception of motion-in-depth in patients with partial or complete cerebral hemispherectomy.

Four patients with functional hemispherectomy, one patient with a complete anatomical hemispherectomy, and one patient with unilateral removal of the temporal, parietal and occipital lobes took part in two sets of experiments designed to investigate their residual sensitivity to motion-in-depth in the hemianopic visual field. Two types of computer-generated visual displays were used; in the first set of experiments, a dot pattern and in the second, a circular checkerboard. These simulated either convergent, divergent or reversed rotational motion. Each set of experiments consisted of two parts; in the first part, electrodermal responses were monitored during stimulus presentation while the subjects performed a simple distracting task. In the second part, subjects were asked to state verbally the direction of stimulus motion. Contrary to expectations, no reliable changes in skin conductance were elicited from any of the subjects by changes in the direction of motion of the component parts of either the dot pattern display or the circular checkerboard display. Furthermore, none of the subjects were able to discriminate the direction of motion of the target patterns when presented in the hemianopic field. The most parsimonious explanation is that the subcortical visual pathways which survive hemispherectomy are unable to process visual information relating to motion in depth.

Adolescent↗
PubMed2005

Imaging of a synchronous neuronal assembly in the human visual brain.

Perception, motion, and cognition involve the formation of cooperative neuronal assemblies distributed over the cerebral cortex. It remains to explore what characterizes the assemblies, their location, and the structural substrate of assembly formation. In this EEG/fMRI study, we describe the response of the visual areas of the two hemispheres in subjects who viewed bilateral iso-oriented (IG) or orthogonally-oriented (OG) moving gratings projected in the two hemifields. The IG stimulus synchronized activity across the hemispheres, as shown by an increased EEG coherence. The increase was restricted to the occipital electrodes and to the beta band. Compared with OG, IG increased the BOLD signal in a restricted territory corresponding to area VP/V4. Within this territory, a linear relation was found between the increased interhemispheric EEG coherence and BOLD. Thus, the increased BOLD localized a trans-hemispheric, synchronous neuronal assembly probably achieved by a callosal cortico-cortical connection. This assembly might reflect an early stage of perceptual grouping since the IG stimulus conforms to Gestalt psychology principles of collinearity and common fate.

Adult↗
PubMed1994

The cerebral activity related to the visual perception of forward motion in depth.

We have used the technique of PET to chart the areas of human cerebral cortex specifically responsive to an optical flow stimulus simulating forward motion in depth over a flat horizontal surface. The optical flow display contained about 2000 dots accelerating in radial directions away from the focus of expansion, which subjects fixated at the centre of the display monitor. Dots remained of constant size, but their density decreased from the horizon, lying across the middle of the screen, to the foreground at the lower screen margin; the top half of the display was void. For the control stimulus the dot motions were randomized, removing any sensation of motion in depth and diminishing the impression of a flat terrain. Comparison of the regional cerebral blood flow (rCBF) elicited by the optical flow and control stimuli was thus intended to reveal any area selectively responsive to the radial velocity field that is characteristic of optical flow in its simplest natural form. Six subjects were scanned, and analysed as a group. Four subjects were analysed as individuals, their PET data being co-registered with MRIs of the cerebrum to localize rCBF changes to individual gyri and sulci. There were three main areas of activation associated with optical flow: the dorsal cuneus (area V3) and the latero-posterior precuneus (or superior parietal lobe) in the right hemisphere, and the occipito-temporal ventral surface, in the region of the fusiform gyrus, in both hemispheres. There was no significant activation of V1/V2, nor of V5. These results show that higher stages of motion take place in both the 'dorsal' and 'ventral' visual pathways, as these are commonly conceived, and that both may be fed by area V3. The information potentially derivable from optical flow concerns the direction of heading, and the layout of the visual environment, a form of three-dimensional structure-from-motion. The perceptual division of labour between the various activated areas cannot be directly inferred, though it is a reasonable supposition that the parietal activation reflects the utility of optic flow for guiding self-motion.

Adult↗
PubMed1993

Vision in stage 5 retinopathy of prematurity after retinal reattachment by open-sky vitrectomy.

Performing vitrectomy in stage 5 retinopathy of prematurity is controversial, partially due to limited anatomical and poor reported visual results. Fifty-five eyes of 50 patients whose retinas were reattached by open-sky vitrectomy in stage 5 retinopathy of prematurity and who were followed up for more than 12 months were analyzed retrospectively to ascertain clinical factors that may influence visual outcome. Vision was evaluated by preferential looking. Visual ability to discriminate stationary objects was obtained in 32 (58.2%) eyes, 18 (32.7%) had motion perception, and five (9.1%) had light stimulus perception. Although visual acuities were relatively low, they were useful to these patients. Age at the time of vitrectomy and the shape of the retinal detachment were found to be important factors in predicting visual prognosis.

Child, Preschool↗
PubMed1999

Mal de debarquement.

MAIN OUTCOME MEASURE: Clinical features of mal de debarquement syndrome. RESULTS: Nearly all respondents were middle-aged women (26 of 27; mean age, 49.3 years). The duration of symptoms ranged from 6 months to 10 years (mean, 3.5 years; SD, 2.5 years). The symptoms were constant in 23 (85%) patients. Neither meclizine hydrochloride nor transdermal scopolamine was helpful. Benzodiazepines were of the most benefit. Balance rehabilitation physical therapy was undertaken by 15 patients, who on average reported a small benefit. CONCLUSIONS: More than double the number of previously reported cases of mal de debarquement syndrome were identified by this study. The syndrome usually occurs in middle-aged women following an ocean cruise. Symptoms are often refractory to vestibular suppressants as well as physical therapy.

Adult↗
PubMed1991

Cortical connections of the caudal subdivision of the dorsolateral area (V4) in monkeys.

Evidence suggests that all primates have rostral and caudal subdivisions in the region of visual cortex identified as the dorsolateral area (DL) or V4. However, the connections of DL/V4 have not been examined in terms of these subdivisions. To determine the cortical connections of the caudal subdivision of DL (DLC) in squirrel monkeys, injections of the neuroanatomical tracers wheat germ agglutinin conjugated to horseradish peroxidase, Diamidino Yellow, and Fluoro-Gold were made in cortex rostral to V II. To aid in delineating the borders of DLC, cortex was also evaluated architectonically. Based on similar patterns of connections, DLC extends from dorsolateral to ventrolateral cortex. DLC receives strong, feedforward input from V II and projects in a feedforward fashion to the rostral subdivision of DL (DLR) and caudal inferior temporal (IT) cortex, including a separate location in the inferior temporal sulcus. DLC has weaker connections with V I, the middle temporal area (MT), cortex rostral to MT in the location of the fundal superior temporal area (FST), cortex dorsal to DLC, ventral cortex rostral to V II, and cortex in the frontal lobe, lateral to the inferior arcuate sulcus. Only lateral DLC has connections with V I, and only dorsolateral DLC has connections with cortex dorsal to DLC. The topographic organization of DLC was inferred from its connections with V II. Thus, dorsolateral DLC represents the lower field, lateral DLC represents central vision, and ventrolateral DLC represents the upper field. Limited observations were made on DLR. Confirming earlier observations (Cusick and Kaas: Visual Neurosci. 1:211, 1988), DLR is paler than DLC myeloarchitectonically. DLR receives only sparse feedforward input from V II, but stronger input from DLC. DLR has strong connections with cortex just rostral to dorsal V II, ventral posterior parietal cortex in the sylvian fissure, MT, the medial superior temporal area, FST, and the inferior temporal sulcus. DLR also shares connections with IT cortex. Thus, while both DLC and DLR are involved in the pathway relaying visual information to IT cortex, an area specialized for object vision, DLR also projects densely to areas such as MT involved in the pathway relaying to posterior parietal cortex, a region specialized for spatial localization and motion perception.

Amidines↗
PubMed2003

Visual function in Huntington's disease patients and presymptomatic gene carriers.

Disturbances of visual cognition, visuomotor performance, and visual memory have been described frequently in Huntington's disease (HD). Early stage visual abnormalities could contribute to these deficits. We evaluated visual processing in 20 control subjects who were non-gene carriers at risk for HD, nine presymptomatic gene-positive subjects, and eight subjects with a recent diagnosis of Huntington's disease. Visual perceptual tests of contrast sensitivity and motion discrimination were used to probe early stage visual processing. Extraocular movements were evaluated in a neurologic examination, and the Digit Symbol test was used to test visual motor performance. Contrast sensitivity did not differ among the three groups. Motion discrimination was impaired in HD subjects but not in the presymptomatic gene carriers when compared to gene noncarriers. Among gene carriers, impaired motion discrimination performance was associated with poorer Digit Symbol performance and extraocular abnormalities. These findings suggest that the early stages of HD are associated with disturbances of motion perception as well as disruptions of visual motor and ocular motor performance.

Adult↗
PubMed1997

The activity in human areas V1/V2, V3, and V5 during the perception of coherent and incoherent motion.

We have used the technique of positron emission tomography to study and compare the cortical activity produced when humans view a pattern of small squares moving incoherently with respect to one another and when the same pattern moves coherently and unidirectionally. A stationary version of the stimulus acted as a control. Our choice of paradigm was inspired by psychophysical models and physiological studies in the macaque monkey which show that directionally selective cells in V5 respond optimally to unidirectional coherent motion, whereas those of V1 respond to motion within their receptive fields, regardless of the motion in surrounding parts. Our results show that human V1/V2, V3, and V5 are all activated by both types of motion stimuli. Incoherent motion, however, proved to be more effective than coherent motion in activating V1/V2 and V5. Thus the higher perceptual salience of unidirectional coherent motion in comparison to incoherent motion is not reflected by any increased activation of human area V5.

Adult↗
PubMed1990

Nature of optokinetic response and zonal organization of climbing fiber afferents in the vestibulocerebellum of the pigmented rabbit. I. The flocculus.

In pigmented rabbits anesthetized with N2O (70%) and halothane (2-4%), Purkinje cells were extracellularly recorded in the flocculus. A large central visual field (60 degrees x 60 degrees) was used to optokinetically stimulate either the ipsi- or contralateral eye, and the direction and velocity selectivities of complex spike responses were examined. For optokinetic stimulation (OKS) delivered to the ipsilateral eye (n = 129), the preferred direction was forward (F, n = 57) or upward (U, n = 37), while the remaining cells (n = 35) showed no response (N). For OKS delivered to the contralateral eye (n = 107), the preferred direction was backward (B, n = 11), downward (D, n = 42) or upward (U, n = 2), and the rest (n = 52) showed N. Cells tested with both eyes (n = 89) fell into five categories based on the preferred direction to ipsi- and contralateral OKS: (1) ipsi-F and contra-B (F/B type, n = 9), (2) ipsi-F but contra-N (F/N type, n = 28), (3) ipsi-U and contra-D (U/D type, n = 13), (4) ipsi-U but contra-N (U/N type, n = 17), and (5) ipsi-N but contra-D (N/D type, n = 22). The optimum velocity was within 0.1-2.0 degrees/s for all cells. On the average, the best response was obtained at 0.2-0.5 degrees/s stimulation. All ipsi-F cells responded to electrical stimulation of the optic tract (OT), while most cells preferring ipsi-U, contra-B and contra-D directions did not respond. No characteristic feature was found in cells innervated with collateralized climbing fiber branches to the nodulus. In the flocculus, cells preferring horizontal orientation (H cells, preferring ipsi-F and/or contra-B directions) were localized in a narrow dorsoventral zone (less than 1.0 mm) along the caudal border of the rostral one third, while those preferring the vertical orientation (V cells, preferring ipsi-U and/or contra-D directions) were in two distinct narrow zones located rostral and caudal to the H cell zone. H and V cells were intermingled in the central portion of the ventral flocculus. These four zones are in good agreement with previously defined H, anterior V, posterior V and R zones, respectively. The results indicate that the subdivision of the flocculus which controls horizontal (vertical) eye movements receives information regarding movements of the visual surround in the horizontal (vertical) orientation through visual climbing fiber afferents, thus being organized in olivo-cortico-nuclear functional units for control of eye movements.

Action Potentials↗
PubMed1990

Nature of optokinetic response and zonal organization of climbing fiber afferents in the vestibulocerebellum of the pigmented rabbit. II. The nodulus.

In pigmented rabbits anesthetized with N2O (70%) and halothane (2-4%), Purkinje cells were extracellularly recorded in the nodulus. Large field (60 degrees x 60 degrees) optokinetic stimulation (OKS) with constant velocity was delivered to either the ipsi- or contralateral eye, and the direction and velocity selectivities of complex spike responses were examined. To ipsilateral OKS (n = 181), the preferred direction was forward (F, n = 72), upward (U, n = 38) or downward (D, n = 10), while the remaining cells (n = 61) showed no response (N). To contralateral OKS (n = 117), the preferred direction was backward (B, n = 22), upward (U, n = 7) or downward (D, n = 22), while the rest (n = 66) showed N. Cells tested with both eyes (n = 95) fell into 8 categories based on the preferred direction to ipsi- and contralateral OKS: (1) ipsi-F and contra-B (F/B type, n = 20), (2) ipsi-F but contra-N (F/N type, n = 12), (3) ipsi-U and contra-D (U/D type, n = 15), (4) ipsi-U but contra-N (U/N type, n = 13), (5) ipsi-N but contra-D (N/D type, n = 1), (6) ipsi-D but contra-N (D/N type, n = 5), (7) ipsi-N but contra-U (N/U type, n = 6), and (8) N to both eyes (N/N type, n = 23). The optimum velocity was in the range 0.1-2.0 degrees/s for all cells responsive to OKS. In the ventral lamella, four medio-laterally aligned zones were demonstrated. In the most medial zone (0-0.5 mm from the midline), the majority of cells showed ipsi-N or contra-N responses. In the second zone (0.5-1.5 mm), most cells preferred ipsi-F or contra-B directions. In the third zone (1.5-2.5 mm), most cells preferred ipsi-U or contra-D directions. In the most lateral zone (2.5-3.5 mm), most cells preferred ipsi-F or contra-B directions. In the dorsal lamella, a longitudinal zone characterized with cells preferring ipsi-U or contra-D directions was found about 1.5-2.5 mm from the midline. This zone seemed to be the continuation of the third zone in the ventral lamella. Cells preferring ipsi-D or contra-U directions were scattered in the medial half of both the dorsal and ventral lamellae.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1990

The effects of contrast on the linearity of spatial summation of simple cells in the cat's striate cortex.

Non-linearities of spatial summation were examined in simple cells in the cat's striate cortex. The degree of non-linearity was assessed from an examination of the waveforms of the responses to moving sinusoidal gratings and was quantified by a measure called relative modulation. Relative modulation was affected little by changes in contrast at either optimal or non-optimal spatial frequencies. The non-linearities of spatial summation exhibited by some simple cells are, therefore, essential. Those simple cells which exhibit linear spatial summation are no less linear at high stimulus contrasts. These results support a 'push-pull' model of simple cell receptive field organization in which ON and OFF centre l.g.n. input is combined both additively and subtractively.

Animals↗
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↗
PubMed1982

The spatial organization of the excitatory regions in the visual receptive fields of the pigeon's optic tectum.

The spatial location of the excitatory regions in the receptive field of cells in the pigeon's optic tectum was analyzed with light and dark edges moving at a constant velocity. The tectal cells were classified into two main groups: 1-cells showing spatially overlapping light and dark excitatory regions in their receptive field (60%); cells showing spatially separated light and dark excitatory regions in their receptive field (32%). A small number of cells discharged only to one sign of contrast. These results were confirmed by testing the cells with light bars of various widths. Latency studies were carried out with single edges moving at a series of constant velocities. In most cases, for any given cell the light and dark edge discharges were shown to have similar latencies. These results also indicate that the relative location of the excitatory regions in the receptive field of most tectal cells was not significantly affected by the latency of the discharges.

Animals↗
PubMed1981

Spatial arrangements of responses by cells in the cat visual cortex to light and dark bars and edges.

Detailed examination is made of the responses of visual cortical cells (area 17, border 17-18 and adjacent area 18) in the anaesthetized cat to stationary flashing bars and to bars (lines) and edges moving at their optimal velocities. Particular attention is given to the receptive field organization of cells in the simple family. While there is good general agreement between the main receptive field subregions revealed by stationary and moving stimuli, the responses to moving light and dark bars, supplemented by the responses to moving light and dark edges, provide a much more rapid, accurate and complete guide to the spatial organization of the receptive fields than do the response profiles to a stationary flashing bar. Moving light and dark bars between them generally reveal more subregions in the receptive fields of simple cells than is evident from the response profiles to a stationary flashing bar, particularly when the receptive fields have many subregions. In addition the responses to moving edges provide a rapid guide to spatial summation across the width of a subregion and the possible antagonistic effects of the next subregion in sequence. Two subclasses of cells in the simple family have been recognized: ordinary simple and fast simple cells. Two cell classes (A-cells and silent periodic cells) having properties intermediate between simple and complex types are discriminated and their properties described.

Animals↗