Abstract:Movements of animals are composed of two fundamental dynamics: discrete and rhythmic movements. Although the movements with distinct dynamics are thought to be differently processed in the CNS, it is unclear how they are represented in the cerebral cortex. Here, we investigated the cortical representation of movement dynamics by developing prolonged transcranial optogenetic stimulation (pTOS) using awake, channelrhodopsin-2 transgenic mice. We found two domains that induced discrete forelimb movements in the f… Show more
“…Although it is not known what exactly the motor map reflects (Histed et al 2009), it has been suggested that motor cortex maps arise from learning-sculpted circuits that support learned movements (Aflalo & Graziano 2006). Indeed, rodent motor cortex appears to be mapped as much by coordinated movements as by somatotopy (Harrison et al 2012, Hira et al 2015, Ramanathan et al 2006), and manipulations of neuromodulators have linked motor maps and motor learning (see the sidebar titled Neuromodulators in the Motor Cortex). NEUROMODULATORS IN THE MOTOR CORTEX
One interesting line of results that comes from studies of rodent motor maps is related to the role of neuromodulators in learning.
The motor cortex is far from a stable conduit for motor commands and instead undergoes significant changes during learning. An understanding of motor cortex plasticity has been advanced greatly using rodents as experimental animals. Two major focuses of this research have been on the connectivity and activity of the motor cortex. The motor cortex exhibits structural changes in response to learning, and substantial evidence has implicated the local formation and maintenance of new synapses as crucial substrates of motor learning. This synaptic reorganization translates into changes in spiking activity, which appear to result in a modification and refinement of the relationship between motor cortical activity and movement. This review presents the progress that has been made using rodents to establish the motor cortex as an adaptive structure that supports motor learning.
“…Although it is not known what exactly the motor map reflects (Histed et al 2009), it has been suggested that motor cortex maps arise from learning-sculpted circuits that support learned movements (Aflalo & Graziano 2006). Indeed, rodent motor cortex appears to be mapped as much by coordinated movements as by somatotopy (Harrison et al 2012, Hira et al 2015, Ramanathan et al 2006), and manipulations of neuromodulators have linked motor maps and motor learning (see the sidebar titled Neuromodulators in the Motor Cortex). NEUROMODULATORS IN THE MOTOR CORTEX
One interesting line of results that comes from studies of rodent motor maps is related to the role of neuromodulators in learning.
The motor cortex is far from a stable conduit for motor commands and instead undergoes significant changes during learning. An understanding of motor cortex plasticity has been advanced greatly using rodents as experimental animals. Two major focuses of this research have been on the connectivity and activity of the motor cortex. The motor cortex exhibits structural changes in response to learning, and substantial evidence has implicated the local formation and maintenance of new synapses as crucial substrates of motor learning. This synaptic reorganization translates into changes in spiking activity, which appear to result in a modification and refinement of the relationship between motor cortical activity and movement. This review presents the progress that has been made using rodents to establish the motor cortex as an adaptive structure that supports motor learning.
“…Several research groups began to take advantage of the semi-transparent nature of the mouse skull by generating large, bi-hemispheric windows through either the intact (Guo et al, 2014), or partially thinned skull (Silasi et al, 2013). Although retraction of the skin alone can have some unwanted effects, such as significant brain cooling in anesthetized mice (Kalmbach and Waters, 2012), the reduced invasiveness offered by transcranial windows has made this the preparation of choice in a number of imaging applications (Cang et al, 2005;Yang et al, 2010;Yoder and Kleinfeld, 2002) including wide-field imaging of hemodynamic signals in anesthetized preparations (Kalchenko et al, 2014;White et al, 2011), and targeted photostimulation in awake (Hira et al, 2009) or behaving mice (Hira et al, 2015). So far, however there have been no detailed methodological descriptions for these preparations, nor has this technique been applied for chronic, wide-field functional imaging in awake mice.…”
Background-Craniotomy-based window implants are commonly used for microscopic imaging, in head-fixed rodents, however their field of view is typically small and incompatible with mesoscopic functional mapping of cortex.New Method-We describe a reproducible and simple procedure for chronic through-bone widefield imaging in awake head-fixed mice providing stable optical access for chronic imaging over large areas of the cortex for months.Results-The preparation is produced by applying clear-drying dental cement to the intact mouse skull, followed by a glass coverslip to create a partially transparent imaging surface. Surgery time takes about 30 minutes. A single set-screw provides a stable means of attachment for mesoscale assessment without obscuring the cortical field of view.Comparison with Existing Methods-We demonstrate the utility of this method by showing seed-pixel functional connectivity maps generated from spontaneous cortical activity of GCAMP6 signals in both awake and anesthetized mice.Conclusions-We propose that the intact skull preparation described here may be used for most longitudinal studies that do not require micron scale resolution and where cortical neural or vascular signals are recorded with intrinsic sensors.
“…Indeed, DM and RM are controlled by distinct corticocortical synaptic circuits (Hira et al . 2015) and more indirect corticospinal pathways contribute to RM (locomotion) in rodents (Miri et al . 2017).…”
Section: Discussionmentioning
confidence: 99%
“…The differences in neural mechanisms underlying DM and RM seem to be specifically related to the initiating and the ending of the movements as ongoing RM also differ from the first (Ikegami et al 2010) and the last cycle of RM (van Mourik & Beek, 2004). Moreover, from animal studies it was suggested that different functional anatomical representations in the motor cortex are accompanied by DM and RM dynamics (Hira et al 2015) and that corticospinal pathways engage in DM and RM differently with regards to movement phase (Miri et al 2017). In conclusion, experimental evidence favours the viewpoint that different neural entities control DM and RM.…”
Section: Introductionmentioning
confidence: 93%
“…Moreover, from animal studies it was suggested that different functional anatomical representations in the motor cortex are accompanied by DM and RM dynamics (Hira et al . 2015) and that corticospinal pathways engage in DM and RM differently with regards to movement phase (Miri et al . 2017).…”
Key points
Discrete and rhythmic dynamics are inherent components of (human) movements.
We provide evidence that distinct human motor cortex circuits contribute to discrete and rhythmic movements. Excitability of supragranular layer circuits of the human motor cortex was higher during discrete movements than during rhythmic movements. Conversely, more complex corticospinal circuits showed higher excitability during rhythmic movements than during discrete movements. No task‐specific differences existed for corticospinal output neurons at infragranular layers.
The excitability differences were found to be time(phase)‐specific and could not be explained by the kinematic properties of the movements.
The same task‐specific differences were found between the last cycle of a rhythmic movement period and ongoing rhythmic movements.
Abstract
Human actions entail discrete and rhythmic movements (DM and RM, respectively). Recent insights from human and animal studies indicate different neural control mechanisms for DM and RM, emphasizing the intrinsic nature of the task. However, how distinct human motor cortex circuits contribute to these movements remains largely unknown. In the present study, we tested distinct primary motor cortex and corticospinal circuits and proposed that they show differential excitability between DM and RM. Human subjects performed either 1) DM or 2) RM using their right wrist. We applied an advanced electrophysiological approach involving transcranial magnetic stimulation and peripheral nerve stimulation to test the excitability of the neural circuits. Probing was performed at different movement phases: movement initiation (MI, 20 ms after EMG onset) and movement execution (ME, 200 ms after EMG onset) of the wrist flexion. At MI, excitability at supragranular layers was significantly higher in DM than in RM. Conversely, excitability of more complex corticospinal circuits was significantly lower in DM than RM at ME. No task‐specific differences were found for direct corticospinal output neurons at infragranular layers. The neural differences could not be explained by the kinematic properties of the movements and also existed between ongoing RM and the last cycle of RM. Our results therefore strengthen the hypothesis that different neural control mechanisms engage in DM and RM.
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