Experimental modification of stepping course in spontaneously initiated locomotor behavior in the crayfish Procambarus clarkii Girard

The stepping course in spontaneously initiated walking of crayfish was quantitatively analyzed using a spherical treadmill system. In complete darkness, some animals stepped either forward or backward at random whereas others showed individually a consistent tendency of stepping in a specific direction although no external sensory cue was provided. The tendency was statistically significant and invariable for at least 6-8 h. When a light stimulus was present in front of the animal, the stepping course tended to be backward or curved forward to avoid the stimulus. Either in complete darkness or in the presence of a light stimulus, the animal's tendency to step in a specific direction could be modified experimentally by applying electrical stimulation to a part of the animal body upon stepping in the preferred direction. The newly acquired tendency of stepping direction could be retained for 6 h and modified again by a similar procedure of electric stimulation. Both before and after modification of the stepping course tendency, animals seldom changed their stepping direction once the walking was initiated. These findings suggest that the stepping course in spontaneously initiated walking is significantly affected by animal's previous experience and could be predetermined at the onset of walking.