Reliability in the location of hindlimb motor representations in Fischer-344 rats

Laboratory investigation

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The purpose of the present study was to determine the feasibility of using a common laboratory rat strain for reliably locating cortical motor representations of the hindlimb.


Intracortical microstimulation techniques were used to derive detailed maps of the hindlimb motor representations in 6 adult Fischer-344 rats.


The organization of the hindlimb movement representation, while variable across individual rats in topographic detail, displayed several commonalities. The hindlimb representation was positioned posterior to the forelimb motor representation and posterolateral to the motor trunk representation. The areal extent of the hindlimb representation across the cortical surface averaged 2.00 ± 0.50 mm2. Superimposing individual maps revealed an overlapping area measuring 0.35 mm2, indicating that the location of the hindlimb representation can be predicted reliably based on stereotactic coordinates. Across the sample of rats, the hindlimb representation was found 1.25–3.75 mm posterior to the bregma, with an average center location approximately 2.6 mm posterior to the bregma. Likewise, the hindlimb representation was found 1–3.25 mm lateral to the midline, with an average center location approximately 2 mm lateral to the midline.


The location of the cortical hindlimb motor representation in Fischer-344 rats can be reliably located based on its stereotactic position posterior to the bregma and lateral to the longitudinal skull suture at midline. The ability to accurately predict the cortical localization of functional hindlimb territories in a rodent model is important, as such animal models are being increasingly used in the development of brain-computer interfaces for restoration of function after spinal cord injury.

Abbreviations used in this paper:ICMS = intracortical microstimulation; SCI = spinal cord injury.

Article Information

Address correspondence to: Shawn B. Frost, Ph.D., Department of Molecular & Integrative Physiology, University of Kansas Medical Center, 3901 Rainbow Blvd., MS 4016, Kansas City, Kansas 66160. email:

Please include this information when citing this paper: published online May 31, 2013; DOI: 10.3171/2013.4.SPINE12961.

© AANS, except where prohibited by US copyright law.



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    A: Schematic diagram of a dorsolateral view of the rat brain showing the location of the hindlimb representation (HL) relative to the forelimb (FL) and face representations in primary motor cortex (M1) of the left hemisphere. B = position of the bregma on the dorsal surface of the skull at midline over the longitudinal convexity. B: Results of ICMS mapping of the hindlimb representation in the left hemisphere in a representative Fischer-344 rat (R33). Circles represent the location of microelectrode penetrations and colors represent the movement evoked by near-threshold electrical stimulation (< 60 μA). In this rat the total hindlimb area measures 2.51 mm2. A = anterior; P = posterior. C: Results of ICMS mapping experiments in the remaining 5 rats. Area measurements of hindlimb movement representations are listed in Table 1. M = medial. The 1-mm scale bar applies to all maps.

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    Graphs showing the distribution of minimum currents required to evoke hindlimb movements (movement thresholds) in each of the 6 rats. Current values for each map were normalized across the range of currents from minimum to maximum, such that minimum (lowest) thresholds = 1 and appear in red and maximum (highest) thresholds = 0 and appear in blue. A MATLAB algorithm was used to interpolate values to create a continuous distribution. A = anterior; L = lateral; M = medial; P = posterior.

  • View in gallery

    Left: Overlay of hindlimb representation borders relative to bregma for each rat. Borders are derived from movement maps illustrated in Fig. 1B and C, and are created by a smoothing algorithm based on locations of individual boundary sites. Right: Hindlimb probability map showing the degree of overlap of hindlimb representations in the sample of 6 rats. Shades of gray and values indicate the number of rats with hindlimb representation at a particular stereotactic location. The darkest region (6) represents the territory in which hindlimb movements are evoked in all 6 rats (100%). The center of the overlap region is located at 2.00 mm posterior and 2.64 mm lateral to the bregma. A = anterior; L = lateral; M = medial; P = posterior.


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