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Improved methods for chronic light-based motor mapping in mice: automated movement tracking with accelerometers, and chronic EEG recording in a bilateral thin-skull preparation.

Silasi G, Boyd JD, Ledue J, Murphy TH - Front Neural Circuits (2013)

Bottom Line: Bilateral maps of forelimb movement amplitude and movement direction were generated at weekly intervals after recovery from cranial window implantation.We found that light pulses of ~2 mW produced well-defined maps that were centered approximately 0.7 mm anterior and 1.6 mm lateral from bregma.Map borders were defined by sites where light stimulation evoked EEG deflections, but not movements.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry, University of British Columbia Vancouver, BC, Canada ; Brain Research Centre, University of British Columbia Vancouver, BC, Canada.

ABSTRACT
Optogenetic stimulation of the mouse cortex can be used to generate motor maps that are similar to maps derived from electrode-based stimulation. Here we present a refined set of procedures for repeated light-based motor mapping in ChR2-expressing mice implanted with a bilateral thinned-skull chronic window and a chronically implanted electroencephalogram (EEG) electrode. Light stimulation is delivered sequentially to over 400 points across the cortex, and evoked movements are quantified on-line with a three-axis accelerometer attached to each forelimb. Bilateral maps of forelimb movement amplitude and movement direction were generated at weekly intervals after recovery from cranial window implantation. We found that light pulses of ~2 mW produced well-defined maps that were centered approximately 0.7 mm anterior and 1.6 mm lateral from bregma. Map borders were defined by sites where light stimulation evoked EEG deflections, but not movements. Motor maps were similar in size and location between mice, and maps were stable over weeks in terms of the number of responsive sites, and the direction of evoked movements. We suggest that our method may be used to chronically assess evoked motor output in mice, and may be combined with other imaging tools to assess cortical reorganization or sensory-motor integration.

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Simultaneous monitoring of light stimulation evoked forelimb movements by accelerometers and cortical depolarization by EEG.(A) A grid of stimulation sites (18 × 23 points) within the chronic cranial window is targeted in random order by a collimated laser beam (asterisk “*” indicates bregma). (B) The magnitude of the EEG deflection for each pixel is represented as a colored heat-map, while black traces show the magnitude of acceleration recorded from the left forelimb (each pixel = 300 μm). The accelerometer and EEG signals from the points marked by the white C and D are expanded in the panels below. (C,D) Example traces of accelerometer (left paw) and EEG signals after stimulation of a site within the motor map (C) and outside the motor map (D) in the right hemisphere (from B). The region shaded in red indicates the threshold for detecting a movement (five times the SD of baseline data). A clearly visible EEG deflection is observed in both examples immediately after the light stimulus (blue bar). The movement response from the motor site (C) was delayed by ~18 ms after stimulus onset.
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Figure 2: Simultaneous monitoring of light stimulation evoked forelimb movements by accelerometers and cortical depolarization by EEG.(A) A grid of stimulation sites (18 × 23 points) within the chronic cranial window is targeted in random order by a collimated laser beam (asterisk “*” indicates bregma). (B) The magnitude of the EEG deflection for each pixel is represented as a colored heat-map, while black traces show the magnitude of acceleration recorded from the left forelimb (each pixel = 300 μm). The accelerometer and EEG signals from the points marked by the white C and D are expanded in the panels below. (C,D) Example traces of accelerometer (left paw) and EEG signals after stimulation of a site within the motor map (C) and outside the motor map (D) in the right hemisphere (from B). The region shaded in red indicates the threshold for detecting a movement (five times the SD of baseline data). A clearly visible EEG deflection is observed in both examples immediately after the light stimulus (blue bar). The movement response from the motor site (C) was delayed by ~18 ms after stimulus onset.

Mentions: Light stimulation was provided by a 473-nm diode pumped solid-state laser (CNI, Optoelectronics, Changchun, China) targeted to the brain through a custom made macroscope (Ayling et al., 2009; Harrison et al., 2009). To achieve square light pulses, the laser was operated in continuous wave and a Pockels cell controlled by Igor Pro software modulated the power and duration of light pulses. A grid of approximately 18 × 23 stimulation points spaced 300 μm apart was superimposed on an image of the cortex and a 5-ms light pulse was delivered to each point in a random order by moving the mouse underneath the beam with an x–y stage controlled by Igor Pro software. Initial maps were generated at multiple laser powers delivered in an interleaved fashion (Figure 2), and all subsequent maps were derived from a single 2 mW laser stimulus delivered to each site. Laser power was measured at the plane of the brain surface with a powermeter (ThorLabs, Newton, NJ, USA; Product: PM100D).


Improved methods for chronic light-based motor mapping in mice: automated movement tracking with accelerometers, and chronic EEG recording in a bilateral thin-skull preparation.

Silasi G, Boyd JD, Ledue J, Murphy TH - Front Neural Circuits (2013)

Simultaneous monitoring of light stimulation evoked forelimb movements by accelerometers and cortical depolarization by EEG.(A) A grid of stimulation sites (18 × 23 points) within the chronic cranial window is targeted in random order by a collimated laser beam (asterisk “*” indicates bregma). (B) The magnitude of the EEG deflection for each pixel is represented as a colored heat-map, while black traces show the magnitude of acceleration recorded from the left forelimb (each pixel = 300 μm). The accelerometer and EEG signals from the points marked by the white C and D are expanded in the panels below. (C,D) Example traces of accelerometer (left paw) and EEG signals after stimulation of a site within the motor map (C) and outside the motor map (D) in the right hemisphere (from B). The region shaded in red indicates the threshold for detecting a movement (five times the SD of baseline data). A clearly visible EEG deflection is observed in both examples immediately after the light stimulus (blue bar). The movement response from the motor site (C) was delayed by ~18 ms after stimulus onset.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3722499&req=5

Figure 2: Simultaneous monitoring of light stimulation evoked forelimb movements by accelerometers and cortical depolarization by EEG.(A) A grid of stimulation sites (18 × 23 points) within the chronic cranial window is targeted in random order by a collimated laser beam (asterisk “*” indicates bregma). (B) The magnitude of the EEG deflection for each pixel is represented as a colored heat-map, while black traces show the magnitude of acceleration recorded from the left forelimb (each pixel = 300 μm). The accelerometer and EEG signals from the points marked by the white C and D are expanded in the panels below. (C,D) Example traces of accelerometer (left paw) and EEG signals after stimulation of a site within the motor map (C) and outside the motor map (D) in the right hemisphere (from B). The region shaded in red indicates the threshold for detecting a movement (five times the SD of baseline data). A clearly visible EEG deflection is observed in both examples immediately after the light stimulus (blue bar). The movement response from the motor site (C) was delayed by ~18 ms after stimulus onset.
Mentions: Light stimulation was provided by a 473-nm diode pumped solid-state laser (CNI, Optoelectronics, Changchun, China) targeted to the brain through a custom made macroscope (Ayling et al., 2009; Harrison et al., 2009). To achieve square light pulses, the laser was operated in continuous wave and a Pockels cell controlled by Igor Pro software modulated the power and duration of light pulses. A grid of approximately 18 × 23 stimulation points spaced 300 μm apart was superimposed on an image of the cortex and a 5-ms light pulse was delivered to each point in a random order by moving the mouse underneath the beam with an x–y stage controlled by Igor Pro software. Initial maps were generated at multiple laser powers delivered in an interleaved fashion (Figure 2), and all subsequent maps were derived from a single 2 mW laser stimulus delivered to each site. Laser power was measured at the plane of the brain surface with a powermeter (ThorLabs, Newton, NJ, USA; Product: PM100D).

Bottom Line: Bilateral maps of forelimb movement amplitude and movement direction were generated at weekly intervals after recovery from cranial window implantation.We found that light pulses of ~2 mW produced well-defined maps that were centered approximately 0.7 mm anterior and 1.6 mm lateral from bregma.Map borders were defined by sites where light stimulation evoked EEG deflections, but not movements.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry, University of British Columbia Vancouver, BC, Canada ; Brain Research Centre, University of British Columbia Vancouver, BC, Canada.

ABSTRACT
Optogenetic stimulation of the mouse cortex can be used to generate motor maps that are similar to maps derived from electrode-based stimulation. Here we present a refined set of procedures for repeated light-based motor mapping in ChR2-expressing mice implanted with a bilateral thinned-skull chronic window and a chronically implanted electroencephalogram (EEG) electrode. Light stimulation is delivered sequentially to over 400 points across the cortex, and evoked movements are quantified on-line with a three-axis accelerometer attached to each forelimb. Bilateral maps of forelimb movement amplitude and movement direction were generated at weekly intervals after recovery from cranial window implantation. We found that light pulses of ~2 mW produced well-defined maps that were centered approximately 0.7 mm anterior and 1.6 mm lateral from bregma. Map borders were defined by sites where light stimulation evoked EEG deflections, but not movements. Motor maps were similar in size and location between mice, and maps were stable over weeks in terms of the number of responsive sites, and the direction of evoked movements. We suggest that our method may be used to chronically assess evoked motor output in mice, and may be combined with other imaging tools to assess cortical reorganization or sensory-motor integration.

Show MeSH
Related in: MedlinePlus