Biomedical subjects

D Bächtold

Publications and source records attributed to D Bächtold.

5 recordsLinked to original sources

PubMed2001

Spatial- and verbal-memory improvement by cold-water caloric stimulation in healthy subjects.

We investigated the effects of unilateral cold-water vestibular stimulation on healthy subjects' performance in two cognitive tasks known to be differentially mediated by the two cerebral hemispheres. In a first experiment (right-hemisphere task), subjects memorized object-location associations while being stimulated with cold water in the left ear or right ear or not at all (control group). In the second experiment (left-hemisphere task), subjects memorized a list of sequentially presented function words while being stimulated in the same manner as the subjects in the first experiment. A recall phase followed each encoding phase. In the first experiment, subjects who had been stimulated in the left ear recalled the object locations significantly faster than subjects who had been stimulated in the right ear and those in the control group. The second experiment yielded the reverse pattern: correct word recognition was faster for subjects who had been stimulated in the right ear than for subjects stimulated in the left ear and those of the control group. We suggest that unilateral caloric stimulation leads to a selective activation of contralateral cerebral structures and speeds up cognitive processes mediated by these structures. These results are discussed with respect to findings in neglect patients and functional-imaging studies in healthy subjects.

Adult↗

PubMed2000

Processing of spatial locations: hemispace effects during encoding but not recall.

Traditionally, functional differences in the visual modality between the two hemispheres are investigated by tachistoscopic procedures. In these experiments, the stimuli reach the contralateral hemisphere first, and results are commonly interpreted on the basis of neuroanatomical access models. However, numerous studies demonstrated that the hemispace where the stimulus is perceived also plays a critical role in producing laterality effects ("hemispace effects"). In the present experiment, subjects were instructed to memorize the relative spatial positions of six figures horizontally aligned on a presentation board. The presentation board was located either to the left, to the right or in front of the subjects (left, right and central learning positions). During a recall phase, each figure was presented in the center of a computer screen and subjects were required to indicate by keypress whether a figure had been located in the left or right half of the presentation board. As in the learning phase, the computer screen was located to the left, the right or in front of the subjects (left, right and central recall positions). We found that the positions of the figures initially memorized in the left hemispace were recalled faster than figures initially memorized in the right hemispace. Hemispatial position during recall had no effect on performance. These results are discussed with respect to hemispheric specialization and theories of hemispace effects.

Adult↗

PubMed2000

Effects of optokinetically induced rotatory self-motion on spatial perception and representation.

OBJECTIVE: Our aim was to investigate the influence of optokinetically induced rotatory self-motion sensation (circular vection [CV]) on asymmetries in real and representational space in normal subjects. BACKGROUND: Vestibular and optokinetic stimulation (particularly when accompanied by rightward CV) can reduce left-sided hemineglect in patients. METHOD: Twenty healthy right-handed men were administered a line bisection (LB) task and a stimulus-response compatibility task monitoring mental representation of space (the RULER task). The RULER task required speeded unimanual decisions ("smaller than 6?" vs. "larger than 6?") to foveally presented numbers between 1 and 11. Both tasks were performed in a baseline condition (no stimulation) and with full-field optokinetic stimulation to induce CV to either side. RESULTS: The bisection marks of both hands were shifted significantly to the left during leftward CV, introducing a pseudoneglect for the left and right hands. Rightward CV did not influence LB. In the RULER task, we found a stimulus-response compatibility, namely, faster right-hand responses to large numbers (i.e., 7-11) and faster left-hand responses to small numbers (i.e., 1-5). Although optokinetic stimulation did not significantly affect subjects' representation of space, the overall pattern of observed deviations was strikingly similar to that obtained in LB. CONCLUSIONS: Optokinetic stimulation affects healthy subjects' exploration and, to a lesser extent, their representation of space. In contrast to previous studies in neglect patients and healthy subjects, we found that leftward CV rather than rightward CV induced a leftward deviation of the subjective midpoint. This discrepancy is most likely a consequence of the exclusively peripheral visual field stimulation in our experiment. We suggest that the leftward deviation during rightward CV described in former studies may be due to the cuing effect of the leftward moving dots in the central visual field. In the absence of these central cues, the direction of CV seems to be the main determining factor for observed hemispatial effects.

Adult↗

PubMed1998

Stimulus-response compatibility in representational space.

Spatial stimulus response (S-R) compatibility designates the observation that speeded reactions to unilateral stimuli are faster for the hand ipsilateral than for the hand contralateral to the sensory hemifield containing the stimulus. In two experiments involving presentation of the numbers 1 to 11 in the center of the visual field we show (1) a left-hand reaction time (RT) advantage for numerals < 6 and a right-hand advantage for those > 6 for subjects who conceive of the numbers as distances on a ruler, and (2) a reversal of this RT advantage for subjects who conceive of them as hours on a clock face. While the results in the first task (RULER) replicate a robust finding from the neuropsychology of number processing (the "SNARC effect") those in the second task (CLOCK) show that extension of the number scale from left to right in representational space cannot be the decisive factor for the observed interaction between hand and number size. Taken together, the findings in the two tasks are best accounted for in terms of an interaction between lateralized mental representations and lateralized motor outputs (i.e. an analog of traditional spatial S-R compatibility effects in representational space). We discuss potential clinical applications of the two tasks in patients with neglect of representational space.

Adolescent↗

PubMed1997

Temporal correlation between neuronal tail ganglion activity and locomotion in the leech, Hirudo medicinalis.

Intracellular and extracellular recordings were performed in the posterior ventral nerve cord of restrained crawling preparations of the medicinal leech, Hirudo medicinalis. Short-latency neuronal activities in the tail ganglion nerves correlated with different phases of crawling behavior. Eight neurons with characteristic activation patterns during crawling were identified morphologically and physiologically in the tail ganglia of 23 preparations. The axons of four of these neurons projected through posterior tail brain nerves; four ascending interneurons had projections in the connectives or in Faivre's nerve. These interneurons are suitable candidates for carrying information between the front end and the tail end of the animal to coordinate the behavioral components during a crawling step.

Action Potentials↗