Latency coding in POm: importance of parametric regimes.

TO THE EDITOR: In a recent Epub issue of the Journal of Neurophysiology, a paper (Masri et al. 2008) appeared in which the authors claim to replicate experiments, but not results, previously obtained in our laboratory (Ahissar et al. 2000; Sosnik et al. 2001). We maintain that Masri et al. 1) did not replicate our experiments, 2) probed the vibrissal system in a different parametric regime, and 3) their results are not inconsistent with ours. In their paper, Masri et al. set out to test a hypothesis formulated on the basis of experiments conducted in our laboratory—that, in the rat trigeminal pathway, response latencies of neurons of the posteromedial thalamic nucleus (POm) correlate positively with stimulation frequencies. Masri et al. claim to have replicated our experiments using stimuli “quantitatively indistinguishable” from those used in our experiments. Based on the assumption that their experimental conditions accurately reproduced ours, they report that the latency coding reported in Ahissar et al. 2000 and Sosnik et al. 2001 could not be replicated and concluded that “stimulation frequency is not reliably reflected in response latencies of POm neurons.” However, there are numerous and significant differences in the experimental procedures used by Masri et al. from those described in our papers, the results and conclusions of which they question (Ahissar et al. 2000, 2001; Sosnik et al. 2001). These differences, described in the following text, 1) prevent direct comparisons between the two studies and 2) result in Masri et al. testing the vibrissal system in a parametric regime that might not be representative of its normal working regime.