Brown Institute for Brain Science

von Frey Filament Test

Rationale of Test

To test tactile sensitivity of rodents and the effect of genetic of pharmacological manipulations on basic sensory function. A variety of disorders with known genetic components show as a common sign, tactile hypersensitivity.

Apparatus

von Frey filament set, video camera

Procedure

Rodents exhibit a paw withdrawal reflex when the paw is unexpectedly touched. The animal indicates sensation by pulling back its paw. 

Touch sensitivity is assessed with von Frey filaments. These filaments are applied to the underside of the paw after the mouse has settled into a comfortable position within a restricted area that has a perforated floor. The filaments are calibrated to flex when the set force is applied to the paw. 

 Filaments are presented in order of increasing stiffness, until a paw withdrawal is detected. The animal is tested again with the same filament as well as the filament just below that which elicited an initial response to insure correct identification of minimal required force to elicit a response.

Interpretation

The need for increased force before an animal demonstrates an appropriate paw withdrawal response indicates a decrease in tactile sensitivity, which may indicate disruptions in sensation. Similarly, an average response to lower applied forces would indicate tactile hypersensitivity.

Relevant Controls

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