Magnitude and phase of three-dimensional (3D) velocity vector: Application to measurement of cochlear promontory motion during bone conduction sound transmission
&NA; Recent measurements of vibrational motion to assess sound transmission through ear structures and skull contents have included three‐dimensional (3D) behavior. The 3D motion of a point has been described with the three orthogonal components in the 3D space. In this article, a method to represent the 3D velocity with the magnitude and phase of the resultant velocity is introduced. This method was applied to the measurement of cochlear promontory motion as an indication of bone conduction (BC) sound transmission. The promontory motions were measured on the ipsilateral and contralateral sides, and the transcranial attenuation and phase delay of the contralateral side relative to the ipsilateral side were calculated. The transcranial attenuation and phase delay calculated with the maximum magnitudes and corresponding phases of the resultant were a better fit to the interaural threshold difference and transcranial time interval between the ipsilateral and contralateral sides as reported in the literature, than the attenuation and phase delay calculated with any individual Cartesian motion component. HighlightsA method to calculate the magnitude and phase of the 3D velocity vector is described.The 3D velocity of a point can be represented by the magnitude and phase of the resultant instead of the magnitudes and phases of the three orthogonal components.The method was applied to the measurement of cochlear promontory motion as an indication of bone conduction (BC) sound transmission.The maximum velocity vector of the cochlear promontory motion is a better descriptor of BC hearing than individual Cartesian components.
Direct measurement of the wavelength of sound waves in the human skull.
The results of a study of the three-dimensional vibration of two dry human skulls in response to harmonic excitation are presented. The vibratory response exhibits three distinct types of motion across the range of audible frequencies. At low frequencies below 1000 Hz, whole-head quasi-rigid motion is seen. At the middle frequencies between 1000 and 6000 Hz, the motion exhibits a series of increasingly complex modal patterns. Above 6000 Hz, the response is wavelike and clear wavefronts can be distinguished in the vibration data. In this regime the relationship between wavelength and frequency is calculated and compared to a number of theories of skull vibration that have been proposed.
Electrophysiological evidence that a subset of midbrain dopamine neurons integrate the reward signal induced by electrical stimulation of the posterior mesencephalon
This study was aimed at determining whether midbrain dopamine (DA) neurons are trans-synaptically activated by rewarding electrical stimulation applied near the midline in the posterior mesencephalon (PM), and in the affirmative, whether the increase in firing was proportional to the rewarding effectiveness of the stimulation. Experiments were performed on male Long-Evans rats trained to lever press to obtain 400 ms trains of cathodal rectangular pulses. Following the training period, curves relating the rates of responding to the stimulation frequencies were determined at two current intensities and reward thresholds were calculated for each animal. Each animal was then anesthetized with urethane (1.2 g/kg, i.p.) and firing rate of DA neurons were recorded before, during, and after each of 50 trains (1 train/3 s) of stimulation to the PM using stimulation parameters that either sustained near threshold responding (rewarding), or failed to sustain responding (non-rewarding), in the behavioral tests. A total of 24 DA cells were recorded from 13 behaviorally trained animals, and of these, 17 (71%) responded to rewarding stimulation by an increase in firing, five (21%) were unresponsive and two (8%) were inhibited. In 12 of the 17 cells that were activated, the increase in firing was proportional to the rewarding effectiveness of the stimulation rather than the total strength of the stimulation. These results provide evidence that a subset of midbrain DA neurons are trans-synaptically activated by rewarding PM stimulation and constitute a second, or subsequent, stage of the reward-relevant pathway that integrates the PM reward signal.