Mechanosensitivity of spinal accessory lobe neurons in the pigeon

In the avian lumbosacral spinal cord there are segmentally organized accessory lobes which protrude into the vertebral canal. These lobes consist of neurons and of glycogen cells. The neurons have been suggested to function as mechanosensitive elements in an extra-labyrinthine sense organ of equilibrium. To test this view, extracellular electrophysiological recordings were done during vibratory stimuli applied to the whole body of anesthetized pigeons. Single unit activity was analyzed with regard to interval distribution (interval histograms) and entrainment to the frequency of the stimulus (autocorrelograms). Most neurons were driven by a 100 or 75 Hz stimulus and there was a tight coupling to the phase of the stimulus. Neurons in the adjacent spinal gray substance did not respond to this stimulus. This strongly supports a mechanosensitive function of the lobe neurons.