J Korean Med Sci.  2014 Apr;29(4):587-592. 10.3346/jkms.2014.29.4.587.

Analysis on Bilateral Hindlimb Mapping in Motor Cortex of the Rat by an Intracortical Microstimulation Method

• Seong HY
• Cho JY
• Choi BS
• Min JK
• Kim YH
• Roh SW
• Kim JH
• Jeon SR

• KMID: 1774467
• DOI: http://doi.org/10.3346/jkms.2014.29.4.587

Abstract

Intracortical microstimulation (ICMS) is a technique that was developed to derive movement representation of the motor cortex. Although rats are now commonly used in motor mapping studies, the precise characteristics of rat motor map, including symmetry and consistency across animals, and the possibility of repeated stimulation have not yet been established. We performed bilateral hindlimb mapping of motor cortex in six Sprague-Dawley rats using ICMS. ICMS was applied to the left and the right cerebral hemisphere at 0.3 mm intervals vertically and horizontally from the bregma, and any movement of the hindlimbs was noted. The majority (80%+/-11%) of responses were not restricted to a single joint, which occurred simultaneously at two or three hindlimb joints. The size and shape of hindlimb motor cortex was variable among rats, but existed on the convex side of the cerebral hemisphere in all rats. The results did not show symmetry according to specific joints in each rats. Conclusively, the hindlimb representation in the rat motor cortex was conveniently mapped using ICMS, but the characteristics and inter-individual variability suggest that precise individual mapping is needed to clarify motor distribution in rats.

Keyword

Hindlimb; Deep Brain Stimulation; Brain Mapping; Motor Cortex

MeSH Terms

Animals
*Brain Mapping
Electric Stimulation
Electrodes
Hindlimb/*physiology
Male
Motor Cortex/*physiology
Rats
Rats, Sprague-Dawley

Figure

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  Fig. 1 A schematic diagram of craniotomy in rat. A median incision was performed on the scalp and the dura mater was exposed after two (left and right) rectangular craniotomy (each 10 mm length and 4 mm width) using the bregma as the reference point. Finally, the dura was removed.

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  Fig. 2 Motor maps in six rats (A-F). The functional mappings obtained by intracortical motor cortex stimulation in bilateral hemisphere were recorded using a matrix table composed of squares corresponding to each stimulation points in the brain (0.3 mm × 0.3 mm). The motor maps were asymmetric, and were not consistent across the six rats. H, hip flexion; K, knee flexion; A, ankle dorsiflexion; FL, forelimb; HL, hind limb; T, tail; W, whiskers.

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  Fig. 3 Summary of motor maps in six rats. Numbers in each squares of a matrix table indicate the numbers of rats that exhibited a motor response at each joint (hip, knee, ankle) in response to intracortical microstimulation of left (A) and right (B) hemisphere. The stimulations of each site usually represent more than two joints (80%). There were thirty points which showing the same joints response in more than four rats, and we found only one point (3.1 mm left lateral from the midline, 1.5 mm posterior to the bregma, indicated by grey highlight) that elicited the same movement (knee flexion) in all six rats. H, hip flexion; K, knee flexion; A, ankle dorsiflexion.

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  Fig. 4 Three-dimensional summary of motor maps in six rats showing the distribution of each joint according ankle (A, B), knee (C, D) and hip (E, F) to intracortical microstimulation of left and right hemisphere. Even though the precise joints stimulated by ICMS do not show symmetricity in each animal, the overall shape of motor maps indicated with numbers of stimulated joint exhibited grossly symmetrical shape.

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