Biomedical subjects

T Brashers-Krug

Publications and source records attributed to T Brashers-Krug.

4 recordsLinked to original sources

PubMed1998

Robot-aided functional imaging: application to a motor learning study.

The purpose of this study was to examine the neural activity underlying an implicit motor learning task. In particular, our goals were to determine whether initial phases of procedural learning of a motor task involve areas of the brain distinct from those involved in later phases of learning the task, and what changes in neural activity coincide with performance improvement. We describe a novel integration of robotic technology with functional brain imaging and its use in this study of implicit motor learning. A portable robotic device was used to generate forces that disturbed the subjects' arm movements, thereby generating a "virtual mechanical environment" that the subjects learned to manipulate. Positron emission tomography (PET) was used to measure indices of neural activity underlying learning of the motor task. Eight health, right-handed male subjects participated in the study. Results support the hypothesis that different stages of implicit learning (early and late implicit learning) occur in an orderly fashion, and that distinct neural structures may be involved in these different stages. In particular, neuroimaging results indicate that the cortico-striatal loop may play a significant role during early learning, and that the cortico-cerebellar loop may play a significant role during late learning.

Adult↗

PubMed1997

Functional stages in the formation of human long-term motor memory.

Previous research has demonstrated that the primate CNS has the ability to learn and store multiple and conflicting visuo-motor maps. Here we studied the ability of human subjects to learn to make reaching movements while interacting with one of two conflicting mechanical environments as produced by a robotic manipulandum. We demonstrate that two motor maps may be learned and retained, but only if the training sessions in the tasks are separated by an interval of approximately 5 hr. If the interval is shorter, learning of the second map begins with an internal model appropriate for the first task and performance in the second task is significantly impaired. Analysis of the after-effects suggests that with a short temporal distance, learning of the second task leads to an unlearning of the internal model for the first. With the longer temporal distance, learning of the second task starts with an unbiased internal model, and performance approaches that of naives. Furthermore, the memory of the consolidated skill lasts for at least 5 months after training. These results argue for a distinct change in the state of resistance of motor memory (to disruption) within a few hours after acquisition. We suggest that motor practice results in memories that have at least two functional components: soon after completion of practice, one component fades while another is strengthened. A further experiment suggests that the hypothetical first stage is not merely a gateway to long-term memory, but also temporary storage for items of information, whether new or old, for use in the near-term. Our results raise the possibility that there are distinct neuronal mechanisms for representation of the two functional stages of motor memory.

Adult↗

PubMed1996

Consolidation in human motor memory.

Learning a motor skill sets in motion neural processes that continue to evolve after practice has ended, a phenomenon known as consolidation. Here we present psychophysical evidence for this, and show that consolidation of a motor skill was disrupted when a second motor task was learned immediately after the first. There was no disruption if four hours elapsed between learning the two motor skills, with consolidation occurring gradually over this period. Previous studies in humans and other primates have found this time-dependent disruption of consolidation only in explicit memory tasks, which rely on brain structures in the medial temporal lobe. Our results indicate that motor memories, which do not depend on the medial temporal lobe, can be transformed by a similar process of consolidation. By extending the phenomenon of consolidation to motor memory, our results indicate that distinct neural systems share similar characteristics when encoding and storing new information.

Adult↗

PubMed1992

p75 nerve growth factor receptor immunoreactivity in the human brainstem and spinal cord.

The distribution of nerve growth factor receptor (NGFR) immunoreactive profiles was investigated in the adult human brainstem and spinal cord using a monoclonal antibody directed against the primate low affinity (p75) NGFR. In the human brainstem, p75NGFR immunoreactive profiles were seen within the mesencephalic and descending nucleus of the trigeminal nerve, the nucleus and tractus solitarius, glossopharyngeal nerve, hypoglossal nucleus, nucleus subtrigeminalis, subnucleus ventralis of the central nucleus of the medulla, nucleus cuneatus and gracilis. At the level of the upper cervical spinal cord, p75NGFR immunoreactive profiles were also seen within the incoming dorsal roots, zone of Lissauer and substantia gelatanosa (lamina II). Virtually no immunoreactivity was associated with cervical spinal cord motor neurons. The demonstration of the p75NGFR in brainstem and spinal cord regions associated with the central transmission of peripheral sensory information suggests that these systems may be influenced by the trophic substance nerve growth factor.

Adult↗