Vibrissae Evoked Forelimb Placing Test
The vibrissae-evoked forelimb placing test (also known as the paw whisker test) is useful for assessing asymmetry in the sensorimotor cortex and striatum. The experimenter holds the animal so that all four limbs hang freely. The vibrissae are stimulated by brushing each side against the edge of a table. This elicits a same-side forelimb response to place the paw on the table top. The rat is allowed ten trials on each side and the percent of successful placements is recorded.
Another variation to the same-side forelimb placing is the cross-midline forelimb placing test. Here, the experimenter turns the animal on its side and holds the same-side forelimb back to inhibit placing. The vibrissae are stimulated and the experimenter records successful placing of the opposite forelimb on the table top. This is useful to assess sensorimotor integration across the right and left hemispheres.
The combination of the same-side and cross-midline tests has been used in assessing the extent of damage to the cerebral hemispheres caused by different brain lesions. For example, striatal damage causes deficit in the affected same-side forelimb placing test. Lesions to the nigrostriatal pathway have been shown to cause a placing deficit to the contralateral forepaw in both same-side and cross-midline vibrissae stimulation.