Biomedical subjects

Simone Cardoso de Oliveira

Publications and source records attributed to Simone Cardoso de Oliveira.

6 recordsLinked to original sources

PubMed2005

Comparing information about arm movement direction in single channels of local and epicortical field potentials from monkey and human motor cortex.

Cortical field potentials have been used for decades in neurophysiological studies to probe spatio-temporal activity patterns of local populations of neurons. Recently, however, interest in these signals was spurred as they were proposed as potential control signals for neuronal motor prostheses, i.e., for devices fit to record and decode brain activity to restore motor functions in paralyzed patients. Little is known, however, about the functional significance of these cortical field potentials. Here we compared information about arm movement direction in two types of movement related cortical field potentials, obtained during a four direction center-out arm reaching paradigm: local field potentials (LFPs) recorded with intracortical micro-electrodes from monkey motor cortex, and epicortical field potentials (EFPs) recorded with macro-electrode arrays subdurally implanted on the surface of the human cerebral cortex. While monkey LFPs showed a typical sequence of positive and negative potential peaks, an initial negative peak was the most salient feature of human EFPs. Individual contralateral LFPs from the monkey motor cortex carried approximately twice as much decoded information (DI) about arm movement direction (median 0.27 bit) as did individual EFPs from the contralateral hand/arm area of primary motor cortex in humans (median 0.12 bit). This relation was similar to the relation between median peak signal-to-noise ratios for directional modulation of movement related potentials (MRPs) of both types of signals. We discuss possible reasons for the observed differences, amongst them epi- vs. intracortical recording and the different electrode dimensions used to measure EFPs and LFPs.

Action Potentials↗

PubMed2005

Encoding of movement direction in different frequency ranges of motor cortical local field potentials.

Recent studies showed that the low-frequency component of local field potentials (LFPs) in monkey motor cortex carries information about parameters of voluntary arm movements. Here, we studied how different signal components of the LFP in the time and frequency domains are modulated during center-out arm movements. Analysis of LFPs in the time domain showed that the amplitude of a slow complex waveform beginning shortly before the onset of arm movement is modulated with the direction of the movement. Examining LFPs in the frequency domain, we found that direction-dependent modulations occur in three frequency ranges, which typically increased their amplitudes before and during movement execution: < or =4, 6-13, and 63-200 Hz. Cosine-like tuning was prominent in all signal components analyzed. In contrast, activity in a frequency band approximately 30 Hz was not modulated with the direction of movement and typically decreased its amplitude during the task. This suggests that high-frequency oscillations have to be divided into at least two functionally different regimes: one approximately 30 Hz and one >60 Hz. Furthermore, using multiple LFPs, we could show that LFP amplitude spectra can be used to decode movement direction, with the best performance achieved by the combination of different frequency ranges. These results suggest that using the different frequency components in the LFP is useful in improving inference of movement parameters from local field potentials.

Action Potentials↗

PubMed2004

Visual feedback reduces bimanual coupling of movement amplitudes, but not of directions.

To what extent does visual feedback shape the coordination between our arms? As a first step towards answering this question, this study compares bimanual coupling in simultaneous bimanual reversal movements that control cursor movements on a vertical screen. While both cursors were visible in the control condition, visual feedback was prevented in the experimental condition by deleting one or both cursors from the screen. Absence of visual feedback for one or both arms significantly increased the reaction times of both arms and the movement amplitude of the occluded arm. Temporal coupling between the arms remained unchanged in all feedback conditions. The same was true for spatial coupling of movement directions. Amplitude coupling, however, was significantly affected by visual feedback. When no feedback for either arm was available, amplitude correlations were significantly higher than when feedback for one or both arms was present. This finding suggests that online visual feedback decreases bimanual amplitude coupling, presumably through independent movement corrections for the two arms. The difference between movement amplitudes and movement directions in their susceptibility to visual feedback supports the idea that they are subserved by different control mechanisms. Analysis of eye movements during task performance revealed no major differences between the different feedback conditions. The eye movements of all subjects followed a stereotypical pattern, with generally only one saccade after target onset, directed towards the average position of all possible targets, irrespective of feedback condition and target direction.

Adult↗

PubMed2004

Control is good; prediction is better?

Franz Mechsner (2004) suggests that movements are exclusively controlled with respect to the effects that they cause in the external world and that motor control can be reduced to prediction of movement effects. Although predictive mechanisms certainly deserve a lot more attention than they have received in the past, the author argues here that prediction and control must necessarily work together to build a flexible and effective motor system.

Humans↗

PubMed2002

Visuomotor transformations affect bimanual coupling.

Interactions between bimanual movements may occur at two different levels: at a visually based level, where movement trajectories are programmed within the visually perceived external space, and at the executional level, through crosstalk of sensorimotor signals arising during movement execution. In order to distinguish between these sources of interactions, we investigated bimanual reversal movements under different conditions of visual feedback. A visuomotor transformation dissociated movement execution from visual appearance on a computer screen. The transformation we used made movements of the same amplitude evoke different excursions, and made movements of different amplitudes entail matched excursions on the screen. The transformed conditions allowed us to study which parameters of bimanual coupling were related to the way movements were executed and which correlated with the visual movement display. We found a clear dissociation between execution-related and visually related bimanual interactions. The assimilation of movement amplitudes was completely execution-related. Whenever movements of different amplitudes were generated, the shorter movement was lengthened, irrespective of how the movements appeared on the feedback screen. In contrast, temporal coordination at the point of movement reversal, as well as trial-by-trial correlations of movement amplitudes, also showed significant effects of the visuomotor transformation, suggesting that these parameters are influenced by visually perceived effects of movements. This dissociation confirms the idea of separate pathways for bimanual interactions and shows that a specific set of bimanual interactions occur at least partly within a visually based external reference frame.

Acculturation↗

PubMed2002

The neuronal basis of bimanual coordination: recent neurophysiological evidence and functional models.

Recent physiological studies of the neuronal processes underlying bimanual movements provide new tests for earlier functional models of bimanual coordination. The recently acquired data address three conceptual areas: the generalized motor program (GMP), intermanual crosstalk and dynamic systems models. To varying degrees, each of these concepts has aspects that can be reconciled with experimental evidence. The idea of a GMP is supported by the demonstration of abstract neuronal motor codes, e.g. bimanual-specific activity in motor cortex. The crosstalk model is consistent with the facts that hand-specific coding also exists and that interactions occur between the motor commands for each arm. Uncrossed efferent projections may underlie crosstalk on an executional level. Dynamic interhemispheric interactions through the corpus callosum may provide a high-level link at the parametric programming level, allowing flexible coupling and de-coupling. Flexible neuronal interactions could also underlie adaptive large-scale systems dynamics that can be formalized within the dynamic systems theory approach. The correspondence of identified neuronal processes with functions of abstract models encourages the development of realistic computational models that can predict bimanual behavior on the basis of neuronal activity.

Arm↗