It is customary to distinguish between sensory neurons and motor neurons, and the distinction between the two is clear and useful when considering function within an intact nervous system. Input of sensory neurons is closely related with the stimuli from the environment. On the other hand, output of motor neurons is related with behavior. The whole nervous system uses information from sensory world to select output to generate behaviors. For achieving this general goal of nervous system, sensory neurons should discriminate new information from sensory stimuli, while motor neurons should select output for behavior. However, there is no known difference at the cellular or molecular levels.
We tested a hypothesis that there are cellular level differences between sensory and motor neurons. Efficient coding theory (Barlow, 1961) suggested that, a sensory neuron should predict its input and maintain homeostatic level of activity, so that neuron can only signal new information (prediction error). A lot of ex-perimental evidences support that this homeostatic mechanism is achieved in many sensory neurons by opening of specific kinds of ion channels and canceling redundant input. On the other hand, it is well known that some motor neurons tend to generate patterns by their intrinsic property. Our hypothesis is that sensory neurons maintain homeostatic excitability and decorrelate patterns, whereas motor neurons generate patterns.
To investigate the sensory and motor difference, we tested our hypothesis in thalamocortical (TC) re-lay neurons, and particularly the function of low voltage activated t-type calcium channels. We recorded neurons in rat brain slices of lateral geniculate nucleus (LGN, sensory nucleus), and ventrolateral nucleus (VL, motor nucleus) using whole cell patch clamp technique.
In TC neurons of both LGN and VL, depolarization from low voltage (-80 and -90 mV) activated T-type calcium current and generated a low threshold spike (LTS). In VL neurons,...