Why is single-cell stimulation in whisker thalamus undetectable?
Electrical stimulation of single tactile afferents from the hand elicits sensations of pressure, touch, vibration, or tickle in humans (Vallbo et al., 1984). Thus, given the detectability of single-cell activity both upstream and downstream of somatosensory thalamus, it is quite unexpected that the animal does not detect increased AP activity in single VPM cells. Moreover, the fact that whiskers are represented by fewer neurons in a thalamic barreloid than in the corresponding cortical barrel column argues that single VPM cells are at least as informative to the brain as single cortical cells. Detection of single-cell stimulation in barrel cortex presumably requires activation of neurons downstream (secondary somatosensory cortex and perhaps frontal lobe), either directly by the stimulated neuron or indirectly through the transsynaptic activation of other neurons in the barrel column. One possible explanation for the lack of single-cell stimulation effects in VPM involves differences i
