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Biomedical subjects

D P Phillips

Publications and source records attributed to D P Phillips.

At least 91 records · Page 5Linked to original sources
PubMed1984

Binaural interactions of single neurons in posterior field of cat auditory cortex.

In the auditory cortex of barbiturate-anesthetized cats, the posterior auditory field (area P) was identified by its tonotopic organization, and single neurons in that field were studied quantitatively with regard to their binaural interactions at their respective best frequencies, using calibrated, sealed stimulating systems. Almost 60% of the neurons studied displayed " summative " binaural interactions in that their responses to binaural, equally intense stimulation of the two ears were stronger than were their responses to monaural stimuli of the same intensity. For these neurons, latent periods were shorter for binaural stimuli than for monaural stimuli. Some field P neurons were sensitive to interaural intensity disparities and manifested that sensitivity in one of two forms. Cells that were excited by stimulation of one ear and inhibited by stimulation of the other typically displayed a sigmoidal relation of spike count to intensive disparity, with spike counts being larger when the disparity favored the contralateral ear. Cells that were unresponsive to monaural stimuli but responded securely to binaural stimuli usually displayed a peaked, nonmonotonic relation of spike count to interaural intensity disparity, with maximal responses being elicited by stimuli with zero or near-zero disparity. Some neurons of low best frequency were sensitive to variations in interaural phase delay. In all cases, this sensitivity was manifested as a cyclical relation of spike count to interaural delay, with the period of the cycle being that of the stimulating tone. The fact that the binaural interactions of field P neurons were similar to those of cells in the primary auditory cortex suggests that the previously described heightened spectral-amplitude selectivity of field P neurons has been achieved without cost to their sensitivity to a variety of parameters of binaural stimulation. The particular sensitivity of cortical neurons to variations in interaural disparities associated with midline or near-midline azimuths might constitute a neural mechanism for the behavioral finding that animals and humans show their greatest acuity in sound localization for stimulus locations in or near the midsagittal plane.

Animals↗
PubMed1983

Spatial receptive fields in the cat inferior colliculus.

Auditory spatial receptive fields of 122 single units in the inferior colliculus of 8 anesthetised cats were studied with free-field acoustic stimuli presented in the frontal hemisphere. The best frequency and best frequency threshold were determined for each unit with the speaker located in a position where the unit responded strongly. The intensity was then raised to 10 dB above threshold at the best frequency and the boundaries of the spatial receptive field were determined. For sounds of low intensity, receptive field size appeared to be a continuum with respect to best frequency. Units of high best frequency had small circumscribed fields located in the contralateral frontal hemifield. The boundaries of receptive fields for units of progressively lower best frequency expanded in all directions. Thus for intermediate frequencies, fields typically filled the contralateral hemifield whereas for low frequencies, units could be activated by stimulation from any position tested. At higher intensities, the boundaries of the receptive fields of units expanded. Circumscribed receptive field centres lay on a line corresponding to the acoustical axis of the contralateral pinna. For these units with small receptive fields, the free-field response to low intensity sounds appeared to be attributable more to the directional properties of the contralateral pinna than to significant binaural interaction.

Acoustic Stimulation↗
PubMed1983

Some features of binaural input to single neurons in physiologically defined area AI of cat cerebral cortex.

1. In the ectosylvian cortex of 24 barbiturate-anesthetized cats, area AI was identified by its frequency organization and the responses to tonal stimuli of single neurons in that field were examined using sealed stimulating systems incorporating calibrated probe microphone assemblies. 2. The responsiveness to monaural and binaural best-frequency stimuli was examined quantitatively for 282 single units in AI. One hundred thirty-nine cells (49%) were excited by independent stimulation of only one ear and were classified as EO cells. In general, the effective monaural excitatory input was derived from the contralateral ear. One hundred ten (39%) neurons were excited by independent stimulation of each ear and were classified as EE units. For these neurons, the contralateral responses were generally stronger, shorter in latency, and lower in threshold than were their ipsilateral responses. Thirty-three cells (12%) gave weak or no responses to monaural stimuli but responded securely to binaural stimuli. These cells were classified as predominantly binaural (PB). 3. Binaural interactions were examined by comparison of the response to binaural, equally intense stimuli to the stronger monaural response. Among EO cells suppression was the most common form of interaction, while for EE cells summation was the more common. Less than 8% of cells were found to be monaural. 4. In electrode penetrations radial to the cortex surface, cells received their stronger or sole monaural excitatory input from a common ear, generally the contralateral. Within such penetrations, however, cells commonly differed with regard to the nature of their input from the other ear and/or in their binaural interactions. 5. Comparison of these data with data previously reported for subcortical auditory nuclei revealed that AI preserves many of the stimulus specificity characteristics of the lower nuclei. The reasons for the preservation of these characteristics at the cortex and the implications of the present data for the binaural column hypothesis are discussed.

Animals↗
PubMed1982

Directionality of sound pressure transformation at the cat's pinna.

The directionality of the cat's pinna was studied by using the amplitude of the cochlear microphonic (CM) as a quantitative indicator of tympanic sound pressure level (SPL). It was found that tympanic SPL varied with the location of a free field stimulator in anechoic space. For high (tonal) frequencies, there was a circumscribed optimal area for tympanic SPL in the frontal ipsilateral sound field, in confirmation of previous findings with other techniques that the pinna has an acoustical axis. The directionality of the pinna, determined from the solid angle enclosed by the 5 dB isointensity-decrement line with respect to the optimal position, increased with frequency. For low tonal frequencies, no circumscribed optimal area in the frontal sound field could be distinguished, and tympanic SPL fell by only 10-12 dB for displacements of 90 degrees into the contralateral sound field. Excision of the pinna abolished the circumscribed optimal areas for tympanic SPL and revealed the pinna produces up to 28 dB amplification of acoustic signals delivered 'on-axis'.

Animals↗
PubMed1982

Representation of the two ears in the auditory cortex: a re-examination.

The current theory of the representation of the two ears in the auditory cortex, namely that both ears are represented in each cerebral cortex and that the contralateral ear receives a stronger representation, is critically reviewed in the light of more recent evidence. On the basis of neurophysiological and behavioral studies in animals and a variety of clinical studies, it is concluded that the notion of contralateral ear dominance in the cortex requires revision, and it is proposed that the contralateral sound field, rather than contralateral ear as such, is represented in each cortex. It is suggested that the contralateral and ipsilateral inputs to the auditory cortex do not so much differ in their relative strengths, but in the qualitative nature of the information they transmit.

Animals↗
PubMed1981

Responses of single neurons in physiologically defined area AI of cat cerebral cortex: sensitivity to interaural intensity differences.

In 15 cats, cortical area AI was defined by its frequency organization, and cells within that field were tested for sensitivity to interaural intensity differences (IIDs) using sealed stimulus delivery systems. Of 39 cells tested quantitatively, 26 were sensitive to IIDs. In 70% of cases, sensitivity to IIDs reflected suppressive binaural interactions, and was manifested as a sigmoidal relation of spike count to IID. For 8 other cells, facilitative binaural interactions generated unit sensitivity to IIDS; three of these neurons demonstrated nonmonotonic dependency of spike count on IID, with peak firing rates at or near 0 dB IID. Analysis of spike count versus IID functions in terms of the auditory azimuths known to generate the IIDs used revealed that the majority of cells were most sensitive to IIDs associated with azimuths in the contralateral sound field. These data are compatible with other evidence on the sensitivity of cortical and brainstem cells to binaural sound localization cues, and suggest that each side of the auditory brain is independently capable of localizing sound sources in the contralateral field.

Animals↗
PubMed1980

The frequency of suicides around major public holidays: some surprising findings.

This paper analyzes the recorded number of U.S. daily suicides, 1972-1976. The paper shows that: there is a dip in suicides on and just before major public holidays; there is a peak in suicides just after these holidays; and, the dip in suicides is somewhat larger than the peak--hence, there is a net decrease in suicides around the holidays. On balance, the holidays appear to reduce the number of suicides, not increase them, as previously believed. In addition, previous research has focussed on the negative psychological impact of holidays. Our findings indicate that holidays have a positive component, which should be taken into account in future research.

Holidays↗
PubMed1979

Acoustic input to single neurons in pulvinar-posterior complex of cat thalamus.

1. Extracellular microelectrode recordings have been made of 429 single neurons in the pulvinar-posterior (Pul-PO) complex and adjacent regions of the thalamus of cats anesthetized with either sodium pentobarbital or alpha-chloralose. Controlled acoustic stimuli were presented by sealed systems incorporating probe microphone assemblies. 2. Neurons in pulvinar, lateralis posterior, and nucleus posterior were unresponsive to acoustic stimulation. Few cells in medial PO were observed to receive acoustic input, while sensitivity to tonal stimuli was a general feature of driven cells in other PO divisions. 3. Cells in lateral PO were generally sharply tuned to stimulus frequency, while the majority of cells in magnocellular medial geniculate and intermediate division of PO were broadly tuned. 4. Neurons in lateral PO and magnocellular medial geniculate had short response latencies to acoustic stimulation. Cells in intermediate division of PO were more often long latency. 5. Divisions of PO could not be differentiated on the basis of their binaural properties. Cells receiving excitatory input from solely the contralateral ear (E/O) or fros with onset discharge patterns showed occlusive binaural interaction properties. For cells with multiple-component discharge patterns, individual response components frequently had different patterns of binaural input and/or interaction. 6. On the basis of their discharge patterns, short latency, and frequency-tuning properties, it is suggested that lateral PO and magnocellular medial geniculate might derive their acoustic input from different divisions of the inferior colliculus. In contrast, the long latencies of units in PO intermediate division suggests a corticofugal input. 7. These data support anatomical parcelations of the Pul-PO complex, and the suggestion that this complex might provide acoustic input to the association cortices is evaluated.

Acoustic Stimulation↗
PubMed1977

Motor vehicle fatalities increase just after publicized suicide stories.

The average increase in motor vehicle fatalities is 9.12 percent in the week after a suicide story. The more publicity given to the story, the greater the rise in motor vehicle deaths thereafter. This rise apparently occurs because suicide stories stimulate a wave of imitative suicides, some of which are disguised as motor vehicle accidents.

Accidents, Traffic↗