PubMed Health⌕ Search

Biomedical subjects

D P Phillips

Publications and source records attributed to D P Phillips.

At least 73 records · Page 4Linked to original sources
PubMed1988

Intracortical connections and their physiological correlates in the primary auditory cortex (AI) of the cat.

We studied the functional and anatomical properties of the intrinsic connections in the primary auditory cortex (AI) of the cat by using physiological mapping and retrograde tracing methods. Our results revealed that a focal microinjection of tracer labeled as many as five intracortical patches in AI. The patches contained labeled pyramidal and non-pyramidal cell types, most of which were clustered in the middle layers. A densely distributed anterograde-like reaction product was present in the superficial layers above the labeled cells. The distribution of the patches was anisotropic, with most patches occurring dorsal, ventral, and anterior to the injection site. We examined the correlation between the characteristic frequency (CF) and binaural response properties of the injected and labeled regions. We found local labeling in regions possessing CFs equivalent to or slightly greater than that of the injected area. This appears to be a specific connection since we were able to predict the general location of many of the patches on the basis of the organization of the isofrequency domains. Patches were more numerous dorsoposterior to the injection site when the isofrequency contours ran obliquely (i.e., dorsoposterior to ventroanterior) across AI. The binaural response properties of the injected and labelled regions, however, were unrelated.

Animals↗
PubMed1988

Effect of tone-pulse rise time on rate-level functions of cat auditory cortex neurons: excitatory and inhibitory processes shaping responses to tone onset.

1. The responses of cat auditory cortex neurons are largely dominated by transient stimulus events, including tone-pulse onset. In addition, these neurons often receive sensitive inhibitory inputs in tone frequency-intensity domains flanking the excitatory one centered at characteristic frequency (CF). These observations suggest that auditory cortex neurons might be sensitive to the spectral splatter that occurs at tone onset due to the tone-pulse envelope shape. 2. To investigate this hypothesis, single neurons in the primary auditory cortex of anesthetized cats were studied for the form of their spike-rate versus tone-level functions using CF tone pulses of different rise times. Stimuli were presented to the contralateral ear using a calibrated, sealed stimulus delivery system. 3. Some neurons with monotonic rate-level functions for conventional (5-10 ms) rise-time tones were relatively insensitive to variations in tone-pulse rise time. Other monotonic neurons showed rate-level functions that became increasingly bell shaped for shorter rise-time stimuli. All neurons with bell-shaped, nonmonotonic rate-level functions for conventional rise-time tones became increasingly nonmonotonic for shorter rise-time signals. In the same neurons, lengthening of tone rise times typically reduced the slope of the high-intensity, descending limb of the rate-level function, in some cases to zero. 4. This pattern of rise-time effects is consistent with previous evidence on the association between rate-level function shape and the presence of inhibitory tone response areas flanking the excitatory one at CF. The present data suggest that cortical neurons are sensitive to the gross shape of the short-term stimulus spectrum at tone onset, and that for many neurons, the nonmonotonic form of CF tone rate level functions may be configured as much by the rate of tone onset as by the plateau amplitude of a tone pulse.

Acoustic Stimulation↗
PubMed1988

A comparison of injury date and death date in 42,698 suicides.

The date of death was compared with the date of injury (the onset of the suicidal act) for 42,698 California suicides, 1973-85. Findings revealed 92.6 per cent of all California suicides occurred within one day of the injury date. Graphs of daily suicides by injury date and by death date displayed essentially identical patterns around the holidays, by date of the week, and after publicized suicide stories. These findings suggest that the difference between date of death and date of injury need not be taken into consideration in the analysis of temporal fluctuations, as was previously supposed.

Adolescent↗
PubMed1987

The impact of televised movies about suicide. A replicative study.

Gould and Shaffer studied suicides by teenagers in the New York City area before and after three fictional films about suicide were televised, and presented evidence suggesting that the films were followed by a significant increase in teenage suicides. Using their methods, we studied teenage suicides in California and Pennsylvania before and after the television broadcast of the same three films. In these states, there was no evidence of an increase in teenage suicides after the films were shown. This remained true when data for New York from the study of Gould and Shaffer were combined with our data from California and Pennsylvania. We conclude that it is premature to be concerned about possibly fatal effects of fictional televised films about suicide.

Adolescent↗
PubMed1987

Responses of single neurons in cat auditory cortex to time-varying stimuli: linear amplitude modulations.

Single neurons in the auditory cortex of anesthetized cats were examined quantitatively for their sensitivity to the sound pressure level of characteristic frequency (CF) tone pulses, and to 6 dB, linear modulations in the amplitude of a continuous CF carrier tone. The direction and rate of amplitude modulation (AM), and the carrier level on which it was imposed, were manipulated parametrically. Studied with amplitude modulations, the majority of neurons responded only to intensity increments. The minimum carrier level upon which an amplitude modulation was able to evoke spike discharges was typically comparable to the tone pulse threshold SPL. For many neurons, an "intensity increment response area", i.e., the domain of AM rate and carrier level conjunctions within which a 6 dB AM was able to evoke discharges, could be delimited. For many neurons, preferred rate of AM drifted from high to low with increases in the carrier level on which the modulation was imposed. The most vigorous responses to AM stimuli often occurred when the carrier levels were associated with the rising slope or the peak of the tone pulse rate intensity function. It may be possible to understand the general form of AM response areas in terms of short-term adaptation, the disposition of excitatory and inhibitory tone pulse response areas, and the spectra of the AM stimuli used.

Acoustic Stimulation↗
PubMed1987

A drop in suicides around major national holidays.

To study the fluctuation of suicides around the holidays, we examined 188,047 U.S. suicides from 1973 to 1979. Correcting for the effects of extraneous variables, such as seasons and days of the week, we found that suicides dropped by an annual average of -102.5 in the period surrounding the holidays. One set of holidays (Memorial Day, Thanksgiving, and Christmas) was associated with an unusually low risk of suicide before, during, and after the holiday. Another set of holidays (New Year's Day, July 4th, and Labor Day) was associated with a low risk of suicide before the holiday and a high risk just afterwards. Almost all demographic groups experienced a low risk of suicide around the holidays: whites, blacks, males, females, retired persons, and persons of working age. Only white teenagers deviated from this pattern. Thus, the evidence does not support the widespread popular assumption that holidays are a risk factor in suicide.

Adult↗
PubMed1987

Stimulus intensity and loudness recruitment: neural correlates.

An abnormally rapid rate of loudness growth for given increments in stimulus intensity is seen both in patients with cochlear pathology and in normal listeners under conditions of wide-spectrum noise masking. The phenomenological similarity between these psychophysical observations raises the question of whether a single mechanism, or set of mechanisms, underlies them. Recent neurophysiological studies in animals have addressed the effects of cochlear pathology and noise masking on the neural correlates of stimulus intensity in the central auditory nervous system. A comparison of the data presented in those studies reveals that there are sequelae of cochlear pathology seen in the discharges of auditory-nerve fibers that might reasonably be expected to contribute to a steepened loudness function. These sequelae are not seen at the same locus in normal animals studied with noise masking paradigms. Noise masking, however, may have effects on the tonal sensitivity of more central neurons that mimic some of the sequelae of cochlear pathology seen in the auditory nerve. These data suggest that the mechanisms underlying the two manifestations of recruitment may be quite different, one having a uniquely cochlear site, while the other reflects purely central processes.

Acoustic Stimulation↗
PubMed1986

Clustering of teenage suicides after television news stories about suicide.

We examined the relation between 38 nationally televised news or feature stories about suicide from 1973 to 1979 and the fluctuation of the rate of suicide among American teenagers before and after these stories. The observed number of suicides by teenagers from zero to seven days after these broadcasts (1666) was significantly greater than the number expected (1555; P = 0.008). The more networks that carried a story about suicide, the greater was the increase in suicides thereafter (P = 0.0004). These findings persisted after correction for the effects of the day of the week, the month, holidays, and yearly trends. Teenage suicides increased more than adult suicides after stories about suicide (6.87 vs. 0.45 percent). Suicides increased as much after general-information or feature stories about suicide as after news stories about a particular suicide. Six alternative explanations of these findings were assessed, including the possibility that the results were due to misclassification or were statistical artifacts. We conclude that the best available explanation is that television stories about suicide trigger additional suicides, perhaps because of imitation.

Adolescent↗
PubMed1986

Representation of the cochlea in primary auditory cortex of the ferret (Mustela putorius).

In seven barbiturate-anesthetized ferrets, we explored the acoustically sensitive cortex with conventional microelectrode mapping techniques. A tonotopically organized field was found whose orientation was such that high tonal frequencies were represented dorsally, and low frequencies ventrally. Within this field, neurons typically had short (12-20 ms) latent periods to first spikes. In conjunction with extant anatomical evidence on the connectivity of this region, these data suggest that this field represents the ferret's primary auditory cortex.

Animals↗
PubMed1986

Spike-rate intensity functions of cat cortical neurons studied with combined tone-noise stimuli.

In the auditory cortex of anesthetized cats, single neurons were studied for their sensitivity to tones presented against backgrounds of continuous wide-spectrum noise. Tone pulses and noise stimuli were mixed acoustically and presented using calibrated, sealed stimulating systems. Data collected were spike-rate intensity functions for tones delivered alone and in the presence of noise. In most neurons, noise of any given intensity induced tone sensitivity shifts that were greatest for frequencies to which the neurons were most sensitive. When the sensitivity loss was in excess of about 15 dB, continuous noise usually caused a steepening of the slope of the tone intensity function. These data suggest that the excitatory response area of a cortical neuron is shaped by multiple, incompletely overlapping inputs of varying sensitivities. In the presence of a continuous noise mask, the disparate thresholds of these inputs may be brought into closer register, resulting in a steepened rate intensity function. These observations may be germane to the neural genesis of the "recruitment" seen in the loudness judgments of normal listeners for masked tones.

Acoustic Stimulation↗
PubMed1985

Responses of single neurones in cat auditory cortex to time-varying stimuli: frequency-modulated tones of narrow excursion.

In the primary auditory cortex of cats anaesthetized with nitrous oxide, single neurones were examined with respect to their responses to tone bursts and linear modulations of the frequency of an on-going continuous tone. Using FM ramps of 2.0 kHz excursion and varying centre frequency, each of 39 neurones was examined for its preference for the direction of frequency change of a ramp whose centre frequency was varied in and around the neurone's response area. Direction preference was strictly associated with the slopes of the cell's spike count-versus-frequency function over the frequency range covered by the ramp. Preferences for upward- and downward-directed ramps were associated with the low- and high-frequency slopes of the spike count function, respectively. The strength of the cell's direction preference was associated with the relative steepness of the spike count function over the frequency range covered by the ramp. The timing of discharges elicited by the frequency modulations was found to be the sum of the cell's latent period for tone bursts plus the time after ramp onset that the stimulus frequency fell within the neurone's response area. The implications of these data for the processing of narrow and broad frequency-modulated ramps are discussed.

Animals↗
PubMed1985

Binaural interactions in cortical area AI of cats reared with unilateral atresia of the external ear canal.

Binaural interactions were recorded in auditory cortical (AI) neurons of anesthetized adult cats that had unilateral atresias created shortly after birth by surgically ligating and cutting one external ear canal. At the time of the recording experiment, the atresia and associated debris were removed and tones were delivered to both tympanic membranes via a sealed and calibrated acoustic system. The majority of neurons recorded were in the cortex ipsilateral to the previously occluded ear. Thresholds for monaural stimulation of either the operated or unoperated ear were within normal range although thresholds to stimulation of the previously operated ear tended to occupy the upper end of the normal distribution. Monotonic and nonmonotonic spike count-vs-intensity functions derived from responses to monaural stimulation of the atretic ear were indistinguishable in their shape from those recorded in normal cats. All binaural classes were represented in our sample in proportions similar to those reported in cats with two normal ears. The forms of the functions relating spike count to interaural intensity differences and interaural phase differences were essentially the same as those seen in normal animals. The main binaural deficit observed under these conditions was a shift in the interaural intensity difference to which an AI neuron was most sensitive. The intensity needed for a stimulus to the atretic ear to participate in the binaural response was as much as 50 dB higher than that at the opposite normal ear in contrast to the nearly equal SPLs required for binaural interactions in cats with two ears intact. It was suggested that elevated thresholds at the previously operated ear could account for much of the shift observed.

Action Potentials↗
PubMed1985

Neurons in the cat's primary auditory cortex distinguished by their responses to tones and wide-spectrum noise.

In the cortex of barbiturate-anesthetized cats, area AI was identified by its tonotopic organization, and single neurons in that field were examined with regard to the shapes of their spike count-versus-intensity functions, the organization of their frequency-intensity response areas, and their responses to wide-spectrum noise, using calibrated sealed stimulating systems. Neurons whose pure tone rate intensity functions were monotonic in shape displayed V-shaped response areas that were open-ended at high tone intensities. In contrast, cells displaying nonmonotonic tone intensity functions tended to have circumscribed response areas; these cells were responsive to tones over limited ranges of both frequency and intensity. Monotonic neurons almost always responded to wide-spectrum noise stimuli, while nonmonotonic neurons often did not. The mean minimum latent period of monotonic cells (14.0 ms) was significantly shorter than that for nonmonotonic neurons (19.1 ms). For those cells that responded to both tones and noise, minimum latent periods for the two stimuli were similar or identical. Monotonic neurons tended to be horizontally segregated from nonmonotonic neurons across AI's middle cortical layers. The implications of these data for the nature of some neural mechanisms underlying the stimulus selectivity of cortical cells are discussed.

Anesthesia, General↗
PubMed1985

Some neural mechanisms in the cat's auditory cortex underlying sensitivity to combined tone and wide-spectrum noise stimuli.

In the auditory cortex of nitrous oxide-anesthetized, muscle-relaxed cats, single neurons were studied for their responsiveness to pure tones that were mixed acoustically with simultaneously gated wide-spectrum noise bursts presented using a calibrated sealed stimulating system. The intensities of both the tone and the noise were systematically varied, with a view to ascertaining the sensitivity of cortical cells to a characteristic frequency tone delivered in the presence of a noise mask. Neurons for which wide-spectrum noise provided a net excitatory influence typically displayed a 'strong-signal capture' effect; that is, the cell's responses were dominated by whichever of the two elements of the combined stimulus was the more effective when tested separately. These cells generally had monotonic tone rate intensity functions. Most of the cells that were suppressed by the noise displayed nonmonotonic pure tone rate intensity functions. When nonmonotonic cells were studied with the combined stimulus, the noise was found to produce an intensity-dependent suppression of their tone-evoked responses that could not be overcome by elevating the tone intensity. In contrast, for the minority of monotonic neurons whose tone-evoked responses were suppressed by noise, that suppression could be overcome by raising the tone intensity. None of the cells in the sample responded in a sustained fashion to continuous noise. In each of 11 cases examined, the effect of a continuous noise mask was to elevate tone thresholds and to prolong latent periods for tones; the magnitude of both of these effects depended on the intensity of the continuous noise mask.

Animals↗
PubMed1985

Temporal response features of cat auditory cortex neurons contributing to sensitivity to tones delivered in the presence of continuous noise.

Single cat auditory cortex neurons have limited intensity dynamic ranges for characteristic frequency (CF) tones. In the presence of continuous wide-spectrum noise, these cells' tone responses undergo a dynamic range shift towards higher SPLs. In the present study, the mechanisms underlying this dynamic range shift were examined by probing the sensitivity of the cells to CF tones delivered at various delays after the onset and/or offset of a long duration noise mask. Fifty cells were studied in the cortex of 7 anesthetized cats using acoustically mixed tonal and noise stimuli presented monaurally to the contralateral ear through a calibrated, sealed stimulating system. For most neurons, the dynamic range shift induced by continuous noise was fully developed in the responses to CF tones delivered 100-250 ms after the onset of a noise mask. For nonmonotonic cells, shorter delays between noise and tone onsets resulted in a profound suppression of tone responses that was consistent with the view that noise stimuli evoke a short latency, but transient, inhibitory response in these neurons. Studies of monotonic cells with short tone delays revealed that the usual excitatory response to noise onset was sometimes followed by a period of inhibition. In most cells, as soon after mask onset that CF tones were able to evoke spike discharges, those responses had latent periods comparable to those of responses to tones of the same SPL delivered in continuous noise. After the offset of an 800 ms noise mask effecting a 15-25 dB dynamic range shift for CF tones, recovery of tone sensitivity to within 5 dB of control levels typically took 50-200 ms. On the basis of these observations, it is argued that in order for a CF tone to excite a cortical neuron after the onset of a noise mask, the tone amplitude must be sufficient to overcome both the transient central neural consequences of noise onset, and a short-term adaptation that is probably peripheral in origin. The implications of these data for the sensitivity of cortical cells to temporally varying stimuli are discussed.

Animals↗
PubMed1984

Responses of single neurons in posterior field of cat auditory cortex to tonal stimulation.

In the auditory cortex of barbiturate-anesthetized cats, the posterior auditory field (field P) was identified by its tonotopic organization, and single neurons in that field were studied quantitatively for their sensitivity to the frequency and intensity of tonal stimuli presented via calibrated, sealed stimulating systems. Field P neurons had narrow, V-shaped, threshold frequency tuning curves. At suprathreshold levels, spike counts were generally greatest at frequencies at or close to the neuron's threshold best frequency (BF). Eighty-six percent of posterior-field neurons displayed spike counts that were a nonmonotonic function of the intensity of a BF tone. Of these, over 90% showed at least a 50% reduction in spike count at high stimulus levels, and almost 20% of nonmonotonic cells ceased responding entirely at high stimulus intensities. The nonmonotonic shape of spike count-versus-intensity profiles was typically preserved across the range of frequencies to which any given neuron was responsive. For some neurons, this had the consequence of generating a completely circumscribed frequency-intensity response area. That is, these neurons responded to a tonal stimulus only if the stimulus was within a restricted range of both frequency and intensity. These response areas showed internal organizations that appeared to reflect one or both of two processes. For some neurons, the optimal sound pressure level for spike counts varied with tone frequency, roughly paralleling the threshold tuning curve. For other neurons, the optimal sound pressure level tended to be constant across frequency despite threshold variations of up to 20 dB. The minimum response latencies of posterior-field neurons were generally in the range of 20-50 ms, while cells in the primary auditory cortex (AI) in the same animals generally had minimum latent periods of less than 20 ms. Comparison of these data with those previously presented for neurons in two other cortical auditory fields suggests that the cat's auditory cortex might show an interfield segregation of neurons according to their coding properties.

Animals↗