Reply to Ahissar et al

REPLY: We are grateful for the comments by Ahissar et al. on our recent manuscript (Masri et al. 2008) and for the opportunity to respond to these comments. Our manuscript focused on testing the hypothesis—formulated by Ahissar and collabo-rators—that the paralemniscal pathway in the rat's vibrissae system functions as a phase-locked loop (PLL) (Ahissar et al. 2000; Sosnik et al. 2001). We emphasize that we do not question the validity of their experimental results or of their analyses. Rather, our goal was to critically test their hypothesis that this sensory system makes use of a PLL mechanism. Two critical predictions emerge from this hypothesis: 1) response latency of neurons in the posteromedial thalamic nucleus (POm) correlates positively with whisking frequency and 2) response duration of these neurons correlates negatively with whisking frequency. In our manuscript we demonstrated that neither of these predictions holds true. In their Letter to the Editor, Ahissar et al. criticize the experimental approach and the analytical tools we used to disprove the latency prediction; they do not comment on our disproving of the response duration prediction. We believe that their critiques are unfounded. Simulated whisking Ahissar et al. attempted to simulate vibrissae movements that occur during " whisking in air " —natural vibrissae movements that occur in the absence of vibrissae contacts with external objects. They do so by applying calibrated air puffs to the vibrissae, to produce vibrissae deflection parameters that replicate kinematics of voluntary whisking. We emphasize that it is highly unlikely that the forces and the resulting transduc-tion events—at the base of the vibrissa follicle— evoked in response to these passive deflections resemble those that occur when the follicle is actively moved by action of the follicular muscles. Rather, these passive deflections mimic contacts of the vibrissae with external objects. Nevertheless, because this was the approach favored by Ahissar and collaborators, we attempted to replicate their paradigm. (We also recorded responses during voluntary whisking in behaving rats; these data are discussed in the following text.) Central to the Ahissar et al. critique is the argument that the discrepancy between their and our results reflects the use of different parameters of vibrissae stimulation. We agree, and we stated so in our manuscript. Specifically, Ahissar et al. stress that our stimuli were produced with air pressures that are stronger than those used in their original studies and they question our use of these stimuli. We …