Biomedical subjects

Christian Dettmers

Publications and source records attributed to Christian Dettmers.

5 recordsLinked to original sources

PubMed2006

Two different reorganization patterns after rehabilitative therapy: an exploratory study with fMRI and TMS.

We used two complementary methods to investigate cortical reorganization in chronic stroke patients during treatment with a defined motor rehabilitation program. BOLD ("blood oxygenation level dependent") sensitive functional magnetic resonance imaging (fMRI) and intracortical inhibition (ICI) and facilitation (ICF) measured with transcranial magnetic stimulation (TMS) via paired pulse stimulation were used to investigate cortical reorganization before and after "constraint-induced movement therapy" (CI). The motor hand function improved in all subjects after CI. BOLD signal intensity changes within affected primary sensorimotor cortex (SMC) before and after CI showed a close correlation with ICI (r = 0.93) and ICF (r = 0.76) difference before and after therapy. Difference in number of voxels and ICI difference before and after CI also showed a close correlation (r = 0.92) in the affected SMC over the time period of training. A single subject analysis revealed that patients with intact hand area of M1 ("the hand knob") and its descending motor fibers (these patients revealed normal motor evoked potentials [MEP] from the affected hand) showed decreasing ipsilesional SMC activation which was paralleled by an increase in intracortical excitability. This pattern putatively reflects increasing synaptic efficiency. When M1 or its descending pyramidal tract was lesioned (MEP from the affected hand was pathologic) ipsilesional SMC activation increased, accompanied by decreased intracortical excitability. We suggest that an increase in synaptic efficiency is not possible here, which leads to reorganization with extension, shift and recruitment of additional cortical areas of the sensorimotor network. The inverse dynamic process between both complementary methods (activation in fMRI and intracortical excitability determined by TMS) over the time period of CI illustrates the value of combining methods for understanding brain reorganization.

Aged↗

PubMed2005

Distributed form of constraint-induced movement therapy improves functional outcome and quality of life after stroke.

OBJECTIVE: To evaluate the effectiveness of a distributed version of constraint-induced movement therapy (CIMT). DESIGN: Within-subjects control intervention study. SETTING: Outpatient rehabilitation center. PARTICIPANTS: Eleven persons with chronic stroke. All had active extension of at least 20 degrees at the wrist and at least 10 degrees for each finger of the more-affected hand. INTERVENTIONS: Intensive motor training of the more-affected arm for 3 hours a day for 20 days; restraint of the other arm for 9.3 hours daily to limit its use. This intervention provides the same amount of training as provided in the conventional CIMT therapy protocol (60 h) but distributes training time over twice the number of days. MAIN OUTCOME MEASURES: Real-world (Motor Activity Log) and laboratory motor activity (Wolf Motor Function Test, Frenchay Arm Test, Nine Hole Peg Test), strength (grip force) and spasticity (Ashworth Scale), and quality of life (QOL; Stroke Impact Scale) were assessed. RESULTS: Participants showed significant improvements in more-affected arm real-world motor activity, laboratory motor activity, strength and spasticity, as well as in some aspects of QOL, up to 6 months after treatment ( P .05). CONCLUSIONS: Distributed CIMT is a promising intervention for improving motor function and QOL in patients with chronic stroke.

Adult↗

PubMed2003

The human action recognition system and its relationship to Broca's area: an fMRI study.

Primate studies have identified populations of neurons that are capable of action recognition. These "mirror neurons" show spiking activity both when the monkey executes or observes a grasping movement. These neurons are located in the ventral premotor cortex, possibly the homologue of "Broca's area" in human. This led to the speculation that action recognition and language production share a common system [Trends Neurosci. 21 (1998), 188]. To test this hypothesis, we combined an action recognition with a language production (VERB) and a grasping movement task (MOVE) by using functional magnetic resonance imaging. Action recognition-related activation was observed in the left inferior frontal gyrus and on the border between the inferior frontal gyrus and precentral gyrus (defined as IFG/PG), the ventral occipitotemporal junction, the superior and inferior parietal cortex, and in the intraparietal sulcus in the left hemisphere. An overlap of activations due to the language production, movement execution, and action recognition was found in the parietal cortex, the left inferior frontal gyrus, and the IFG-PG border (IFG/PG). The activation peaks of action recognition and verb generation were always different in single subjects, but no consistent spatial relationship was detected, in accord with the hypothesis that action recognition and language production share a common functional architecture.

Algorithms↗

PubMed2002

Visuomotor control within a distributed parieto-frontal network.

The aim of this functional magnetic resonance imaging study was to investigate differences in visuomotor control with increasing task complexity. Twelve right-handed volunteers were asked to perform their signature under different degrees of visual control: internally generated movement with closed eyes, signing with open eyes, tracking the line of the projected signature forwards, and tracking the line of the projected signature backwards. There was a gradual onset and disappearance of activation within a distributed network. Parietal, lateral and medial frontal brain areas were activated during all conditions, confirming the involvement of a parieto-frontal system. The weight of activation shifted with increasing task complexity. Internally generated movements activated predominantly the inferior parietal lobule and the ventral premotor cortex, as well as the rostral cingulate area, pre-supplementary motor area (pre-SMA) and SMA proper. Opening the eyes reduced SMA and cingulate activation and activated increasingly the occipito-parietal areas with higher task complexity. Visually guided movements produced an activation predominantly in the superior parietal lobule and dorsal premotor cortex. This study bridges human activation studies with the results of neurophysiological studies with monkeys. It confirms a gradual transition of visuomotor control with increasing task complexity within a distributed parieto-frontal network.

Adult↗

PubMed2002

Reduction of excitability ("inhibition") in the ipsilateral primary motor cortex is mirrored by fMRI signal decreases.

Functional magnetic resonance imaging (fMRI) was used to investigate how focal cortical inhibition affects the blood oxygen level-dependent (BOLD) signal. Phasic low force pinch grip reduces excitability of the ipsilateral primary motor cortex. This task was used to study BOLD signal changes during inhibition. Six right-handed normal volunteers participated in the study. They were asked to perform a right-handed pinch grip repetitively at 1 Hz and 5% of their individual maximal voluntary contraction (MVC). Data were acquired with a 1.5 Tesla Magnetom and continuous multislice T2*-weighted images. The contralateral primary motor cortex (M1) revealed an activation in the knob-shaped hand representation of the central sulcus area. More importantly, a decreased (often referred to as "negative") BOLD signal in the ipsilateral M1 was observed. We suggest phasic low force pinch grip as a reproducible, easy model of focal inhibition. Decreased cortical excitability presents as decreased BOLD signal using fMRI.

Adult↗