Biomedical subjects

K V Thilo

Publications and source records attributed to K V Thilo.

9 recordsLinked to original sources

PubMed2002

Repetitive transcranial magnetic stimulation for Tourette syndrome.

In a single-blinded, placebo-controlled, crossover repetitive transcranial magnetic stimulation (rTMS) trial, 16 patients with Gilles de la Tourette syndrome (GTS) received in random sequence 1 Hz motor, premotor, and sham rTMS, which each consisted of two 20-minute rTMS sessions applied on 2 consecutive days. In the 12 patients who completed the trial, there was no significant improvement of symptoms after any of the rTMS conditions as assessed with the Motor tic, Obsessions and compulsions, Vocal tic Evaluation Survey.

Anxiety↗

PubMed2002

Parietal magnetic stimulation delays visuomotor mental rotation at increased processing demands.

Visuomotor rotation (VMR) is a variant of the classic mental rotation paradigm. Subjects perform a center-out arm reaching movement, with the instruction to point clockwise or anticlockwise away from the direction of a reaction signal by a prespecified amount. Like classic mental rotation (MR) tasks, there is a linear relationship between reaction time (RT) and required angle of rotation (angular disparity). Although functional imaging studies have consistently demonstrated parietal activations centered around the intraparietal sulcus during MR tasks, the involvement of parietal cortex in VMR has not been investigated. The aim of the present experiments was to test in human subjects whether VMR also involves activity in parietal areas. We used short trains of transcranial magnetic stimulation (TMS) to produce a temporary "virtual lesion" of the posterior parietal cortex (PPC) around the intraparietal sulcus during the reaction period of a VMR task. Four pulses of 20-Hz rTMS were applied to the left PPC, right PPC, or vertex (control condition) 100 ms after the presentation of an instruction cue. Reaction times (RTs) were evenly prolonged by right or left parietal TMS compared with vertex stimulation, but only for large angles of rotation, and without affecting the spatial accuracy of the final response. A control experiment showed that parietal rTMS did not impair visual perception or the ability to judge the size of visual angles. The data thus provide evidence for bilateral involvement of the PPC in VMR that increases with processing demands.

Adult↗

PubMed2002

Positional down beating nystagmus in 50 patients: cerebellar disorders and possible anterior semicircular canalithiasis.

OBJECTIVES: To clarify the clinical significance of positional down beat nystagmus (pDBN). METHODS: A discussion of the neuro-otological findings in 50 consecutive patients with pDBN. RESULTS: In 38 patients there was evidence of CNS disease (central group) but in 12 there was not (idiopathic group). In the CNS group, presenting symptoms were gait, speech, and autonomic dysfunction whereas in the idiopathic group patients mostly reported positional vertigo. The main neurological and oculomotor signs in the CNS group were explained by cerebellar dysfunction, including 13 patients with multiple system atrophy. In patients with multiple system atrophy with a prominent extrapyramidal component, the presence of pDBN was helpful in the differential diagnosis of atypical parkinsonism. No patient with pDBN had the Arnold-Chiari malformation, a common cause of constant down beat nystagmus (DBN). In the idiopathic group, the pDBN had characteristics which suggested a peripheral labyrinthine disorder: vertigo, adaptation, and habituation. In six patients an additional torsional component was found (concurrently with the pDBN in three). Features unusual for peripheral disorder were: bilateral positive Dix-Hallpike manoeuvre in nine of 12 patients and selective provocation by the straight head-hanging manoeuvre in two. CONCLUSION: It is argued that some patients with idiopathic pDBN have benign paroxysmal positional vertigo (BPPV) with lithiasis of the anterior canal. The torsional component may be weak, because of the predominantly sagittal orientation of the anterior canal, and may not be readily seen clinically. Nystagmus provocation by bilateral Dix-Hallpike and straight head-hanging may be explained by the vertical upwards orientation of the ampullary segment of the anterior canal in the normal upright head position. Such orientation makes right-left specificity with the Dix-Hallpike manoeuvre less important than for posterior canal BPPV. This orientation requires a further downwards movement of the head, often achieved with the straight head-hanging position, to provoke migration of the canaliths. The straight head-hanging manoeuvre should be carried out in all patients with a history of positional vertigo and a negative Dix-Hallpike manoeuvre.

Adult↗

PubMed2001

Influence of action and expectation on visual control of posture.

Previous studies have shown that human subjects presented with a moving visual environment initiate a postural re-adjustment in the direction of motion. The present study investigated how active control or expectation of the displacement of a visual scene affects this postural response. Center of foot pressure (COP) and head displacement were recorded using a sway platform and a tracking system, respectively. The subjects faced a visual scene (1 x 1 m, at a distance of 45 cm) which moved transiently (with a velocity of 1 cm/s) in a direction parallel to the interaural axis. When the displacement of the visual scene was under the active control of the subjects, visually induced body sway was strongly inhibited, in comparison with the response to unexpected stimuli. Prior knowledge of the characteristics of the forthcoming displacement was sufficient, in most subjects, to reduce postural re-adjustment, even when subjects did not exert active control. Finally, the visually induced postural response was strongly reduced even when subjects only triggered the stimulus, without any knowledge about the direction of motion. In conclusion, it appears that although vision is of primary importance in the control of postural orientation, high level processes such as expectation can modulate its impact by providing cues as to whether forthcoming visual flow is the consequence of self-motion or object-motion.

Adult↗

PubMed2001

Transcranial magnetic stimulation of medial-frontal cortex impairs the processing of angry facial expressions.

Growing evidence suggests that the recognition of different emotional states involves at least partly separable neural circuits. Here we assessed the discrimination of both anger and happiness in healthy subjects receiving transcranial magnetic stimulation (TMS) over the medial-frontal cortex or over a control site (mid-line parietal cortex). We found that TMS over the medial-frontal cortex impairs the processing of angry, but not happy, facial expressions of emotion.

Adult↗

PubMed2000

Changes in horizontal oculomotor behaviour coincide with a shift in visual motion perception.

During full-field rotation of the visual field, subjects commonly experience an initial perception of object-motion which 'switches' to a perception of self-motion. We studied the characteristics of the horizontal optokinetic nystagmus responses evoked by a moving visual stimulus in these two perceptual states over a range of stimulus velocities. During self-motion perception mean eye position was found to shift more in the direction of the newly appearing stimulus elements with a slight reduction in slow phase gain in comparison to the nystagmus evoked during object-motion perception. The results may reflect a modified strategy of spatial attention with increased emphasis on anticipatory eye movements during visually induced self-motion perception.

Adult↗

PubMed2000

Autonomic response to real versus illusory motion (vection).

This study explored the cardiovascular responses to illusions of self-motion (vection) induced in normal subjects according to the hypothesis that vection may be a model for vertigo in vestibular disease. Responses were obtained from 10 men who were exposed to rapid tilts of 20 degrees and 30 degrees rolling from the upright position down to the right or left shoulder. These responses were compared with those evoked during the illusion of roll-tilt vection provoked by a torsionally rotating visual field. Comparisons were made between 10-second data epochs before and after stimulus onset. In response to vection, blood pressure (BP) in the radial artery rose consistently in six subjects, and in all of these, a pressor response to real tilt was also observed. The remaining four subjects consistently had decreased BP in response to vection, and their BPs were affected little by tilt. Subjects whose BP increased with vection and tilt may have been dominated by tendency to arousal, whereas those whose BP decreased may reveal the more appropriate response to tilt from the upright position, which is a decrease in BP. This may reflect individual stereotypes and differences in the relative contributions of somatosensory and vestibular control of autonomic regulation.

Adaptation, Physiological↗

PubMed2000

Visual control of postural orientation and equilibrium in congenital nystagmus.

PURPOSE: To investigate how humans with congenital nystagmus (CN) use visual information to stabilize and orient their bodies in space. METHODS: Center of foot pressure (COP) and head displacements in the lateral plane were recorded using a sway platform and Schottky barrier photodetector, respectively. In experiment 1, a comparison was made of the oscillatory characteristics of body sway with eyes open compared with eyes closed. Experiment 2 studied the postural readjustments made in response to absolute or relative motion (motion parallax) of objects in the visual scene, generated by lateral displacement of background scenery. RESULTS: Experiment 1 revealed that subjects with CN were not able to use visual information to stabilize COP but were able to stabilize the head at frequencies lower than 1 Hz. Experiment 2 showed that in response to the displacement of a visual display, for both absolute motion and motion parallax, subjects with CN reoriented their body in space in a manner similar to control subjects. CONCLUSIONS: The results suggest that despite involuntary eye movements, subjects with CN use orientation cues to control their posture, but not dynamic cues useful to control the rapid oscillations that are particularly important at the level of COP. These findings suggest that in CN, visual control of posture is restricted by low-frequency sampling of the visual scene.

Adult↗

PubMed1999

Torsional eye movements are facilitated during perception of self-motion.

Visual motion in the roll plane elicits torsional optokinetic nystagmus (tOKN) with intermittent periods of illusory, contradirectional self-motion (circularvection, CV). The CV may also have a component of whole-body tilt if the axis of stimulus rotation is not aligned with the direction of gravity. We report how the characteristics of tOKN are affected by the presence of CV. Subjects had their eye movements recorded by VOG whilst viewing a full-field stimulus rotating at 30-60 degrees/s about their naso-occipital axis. They were tested in upright and supine posture and signalled the presence-absence of CV with a pushbutton. In both postures, during CV, tOKN slow-phase gain was found to be enhanced and average torsional eye position shifted in the direction opposite to stimulus rotation. When supine, slow-phase gain was greater than when upright both during the perception of object-motion and during CV. The effects may be explained in terms of a relegation of restraining vestibular input to the torsional oculomotor system during CV and illusory tilt.

Adult↗