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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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Average motor maps for individual mice. To assess inter-subject variability, motor output from the three mapping sessions was averaged to create an average motor map for each mouse. The dorsal view of the cranial window is shown on the right with the mapped region outlined in white (asterisk “*” indicates bregma; each pixel = 300 μm).
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Figure 5: Average motor maps for individual mice. To assess inter-subject variability, motor output from the three mapping sessions was averaged to create an average motor map for each mouse. The dorsal view of the cranial window is shown on the right with the mapped region outlined in white (asterisk “*” indicates bregma; each pixel = 300 μm).

Mentions: In order to assess the stability of our chronic window preparation over time we quantified the stability of motor and EEG maps over repeated mapping sessions spaced at least 1 week apart (Figure 4A). When we averaged all active pixels in the motor maps, there were no significant changes in average motor output, motor map size, or relative map location (center of gravity) over time (p > 0.2966, n = 5 mice; Figure 4C). Importantly, there was also no significant change in the magnitude of the EEG depolarization suggesting that light penetration and cortical excitability were equivalent during the three mapping sessions (p = 0.903). The direction of the evoked movements also showed clear consistency across time, as most movements were in the anterior direction in the horizontal plane, with a slight elevation in the vertical plane (Figure 4B). To show the qualitative features of motor map topography in all animals, we averaged the motor maps from three mapping sessions for each animal (Figure 5; n = 5 mice). By summing all active pixels (accelerations greater than five times the SD of baseline data) from each forelimb map we found the average center of gravity was located 1.65 mm lateral and 0.735 mm anterior from bregma, and the average area of the forelimb motor map was 3.02 mm2 (n = 5 mice).


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)

Average motor maps for individual mice. To assess inter-subject variability, motor output from the three mapping sessions was averaged to create an average motor map for each mouse. The dorsal view of the cranial window is shown on the right with the mapped region outlined in white (asterisk “*” indicates bregma; each pixel = 300 μm).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Average motor maps for individual mice. To assess inter-subject variability, motor output from the three mapping sessions was averaged to create an average motor map for each mouse. The dorsal view of the cranial window is shown on the right with the mapped region outlined in white (asterisk “*” indicates bregma; each pixel = 300 μm).
Mentions: In order to assess the stability of our chronic window preparation over time we quantified the stability of motor and EEG maps over repeated mapping sessions spaced at least 1 week apart (Figure 4A). When we averaged all active pixels in the motor maps, there were no significant changes in average motor output, motor map size, or relative map location (center of gravity) over time (p > 0.2966, n = 5 mice; Figure 4C). Importantly, there was also no significant change in the magnitude of the EEG depolarization suggesting that light penetration and cortical excitability were equivalent during the three mapping sessions (p = 0.903). The direction of the evoked movements also showed clear consistency across time, as most movements were in the anterior direction in the horizontal plane, with a slight elevation in the vertical plane (Figure 4B). To show the qualitative features of motor map topography in all animals, we averaged the motor maps from three mapping sessions for each animal (Figure 5; n = 5 mice). By summing all active pixels (accelerations greater than five times the SD of baseline data) from each forelimb map we found the average center of gravity was located 1.65 mm lateral and 0.735 mm anterior from bregma, and the average area of the forelimb motor map was 3.02 mm2 (n = 5 mice).

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