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| 2. |
- Omrani, Mohsen, et al.
(författare)
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Perturbation-evoked responses in primary motor cortex are modulated by behavioral context
- 2014
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 112:11, s. 2985-3000
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Tidskriftsartikel (refereegranskat)abstract
- Corrective responses to external perturbations are sensitive to the behavioral task being performed. It is believed that primary motor cortex (M1) forms part of a transcortical pathway that contributes to this sensitivity. Previous work has identified two distinct phases in the perturbation response of M1 neurons, an initial response starting similar to 20 ms after perturbation onset that does not depend on the intended motor action and a task- dependent response that begins similar to 40 ms after perturbation onset. However, this invariant initial response may reflect ongoing postural control or a task- independent response to the perturbation. The present study tested these two possibilities by examining if being engaged in an ongoing postural task before perturbation onset modulated the initial perturbation response in M1. Specifically, mechanical perturbations were applied to the shoulder and/ or elbow while the monkey maintained its hand at a central target or when it was watching a movie and not required to respond to the perturbation. As expected, corrective movements, muscle stretch responses, and M1 population activity in the late perturbation epoch were all significantly diminished in the movie task. Strikingly, initial perturbation responses (<40 ms postperturbation) remained the same across tasks, suggesting that the initial phase of M1 activity constitutes a task- independent response that is sensitive to the properties of the mechanical perturbation but not the goal of the ongoing motor task.
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| 3. |
- Pruszynski, J Andrew, et al.
(författare)
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Goal-dependent modulation of fast feedback responses in primary motor cortex
- 2014
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Ingår i: Journal of Neuroscience. - : Society for neuroscience. - 0270-6474 .- 1529-2401. ; 34:13, s. 4608-4617
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Tidskriftsartikel (refereegranskat)abstract
- Many human studies have demonstrated that rapid motor responses (i.e., muscle-stretch reflexes) to mechanical perturbations can be modified by a participant's intended response. Here, we used a novel experimental paradigm to investigate the neural mechanisms that underlie such goal-dependent modulation. Two monkeys positioned their hand in a central area against a constant load and responded to mechanical perturbations by quickly placing their hand into visually defined spatial targets. The perturbation was chosen to excite a particular proximal arm muscle or isolated neuron in primary motor cortex and two targets were placed so that the hand was pushed away from one target (OUT target) and toward the other (IN target). We chose these targets because they produced behavioral responses analogous to the classical verbal instructions used in human studies. A third centrally located target was used to examine responses with a constant goal. Arm muscles and neurons robustly responded to the perturbation and showed clear goal-dependent responses ∼35 and 70 ms after perturbation onset, respectively. Most M1 neurons and all muscles displayed larger perturbation-related responses for the OUT target than the IN target. However, a substantial number of M1 neurons showed more complex patterns of target-dependent modulation not seen in muscles, including greater activity for the IN target than the OUT target, and changes in target preference over time. Together, our results reveal complex goal-dependent modulation of fast feedback responses in M1 that are present early enough to account for goal-dependent stretch responses in arm muscles.
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| 4. |
- Pruszynski, J. Andrew, et al.
(författare)
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Primary motor cortex underlies multi-joint integration for fast feedback control
- 2011
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Ingår i: Nature. - London : Macmillan Journals. - 0028-0836 .- 1476-4687. ; 478:7369, s. 387-390
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Tidskriftsartikel (refereegranskat)abstract
- A basic difficulty for the nervous system is integrating locally ambiguous sensory information to form accurate perceptions about the outside world(1-4). This local-to-global problem is also fundamental to motor control of the arm, because complex mechanical interactions between shoulder and elbow allow a particular amount of motion at one joint to arise from an infinite combination of shoulder and elbow torques(5). Here we show, in humans and rhesus monkeys, that a transcortical pathway through primary motor cortex (M1) resolves this ambiguity during fast feedback control. We demonstrate that single M1 neurons of behaving monkeys can integrate shoulder and elbow motion information into motor commands that appropriately counter the underlying torque within about 50 milliseconds of a mechanical perturbation. Moreover, we reveal a causal link between M1 processing and multi-joint integration in humans by showing that shoulder muscle responses occurring 50 milliseconds after pure elbow displacement can be potentiated by transcranial magnetic stimulation. Taken together, our results show that transcortical processing through M1 permits feedback responses to express a level of sophistication that rivals voluntary control; this provides neurophysiological support for influential theories positing that voluntary movement is generated by the intelligent manipulation of sensory feedback(6,7).
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