Note on the tonotopic organization in the cat medial geniculate body: influence of sampling of units.

The tonotopic organization observed in the present study for the pars lateralis (LV) of the medial geniculate body (MGB) in nitrous oxide anesthetized cats is generally consistent with that previously reported under barbiturate anesthesia. The present data, however, provide evidence for local deviations in characteristic frequency (CF) using appropriate sampling procedures of single units. Although the majority of pairs of units recorded simultaneously with the same microelectrode showed comparable CFs, a few pairs of such neighbouring units displayed CF disparities of up to 1.5 octaves. In addition, some units characterized by an elevated threshold had a CF deviating significantly from the general CF progression observed for the majority of units having low thresholds. This study points out the influence of the sampling procedure on the quality of the tonotopic organization observed in the MGB in addition to a possible effect of the level of anesthesia.