To elucidate the role of trigeminal input on the olfactory system, field-evoked potentials were measured following electrical stimulation of the nasociliary branch of the trigeminal nerve in the olfactory-related structures in the rat brain. Significant potential changes were recorded in the mediodorsal nucleus of the thalamus and the lateral hypothalamic area. In the mediodorsal nucleus of the thalamus, the neurons responding to olfactory bulb electrical stimulation also responded to trigeminal nerve stimulation. Single neuronal responses of mediodorsal thalamic neurons following odorant stimulation were enhanced by blockade of the trigeminal nerve with procaine. These results suggest that olfactory and trigeminal pathways converge on the same neural elements within the mediodorsal nucleus of the thalamus and that the trigeminal input may modulate olfactory input in this nucleus.

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The literature of frequency and intensity analysis in audition is reviewed. An experimental study of the measurement of cochlear microphonics of each turn of the cochlea to frequency and intensity in guinea pigs is presented. The observation demonstrates that the amplitudes of the cochlear microphonics for low intensity tones are compatible with von BÉKÉSY’S observation of the point of maximum displacement of the basilar membrane according to frequency. However, at high intensities the greater amplitude of the cochlear microphonics at the basal turn regardless of frequency suggests that either the amplitude of displacement of the basilar membrane is greatest at the basal turn for all frequencies or that factors other than the degree of displacement of the basilar membrane are involved in determination of the amplitude of the cochlear microphonics.