Search PubMed⌕ Search

Biomedical subjects

T McGee

Publications and source records attributed to T McGee.

At least 19 recordsLinked to original sources
PubMed1999

Thalamic asymmetry is related to acoustic signal complexity.

Hemispheric asymmetries in response to speech sounds are well documented. However, it is not known if these asymmetries reflect only cortical hemispheric specialization to language or whether they also reflect pre-conscious encoding of signals at lower levels of the auditory pathway. This study examined differences in neural representations of signals with acoustic properties inherent to speech in the left versus right side of the thalamus. Specifically, 2000 Hz tone bursts, clicks and synthesized forms of the phoneme /da/ were presented to anesthetized guinea pigs. Evoked responses were recorded simultaneously from aggregate cell groups in the left and right medial geniculate bodies. Results showed an asymmetric response to complex auditory stimuli between the left versus right auditory thalamus, but not to the simple tonal signal. Moreover, asymmetries differed in male versus female animals.

Acoustic Stimulation↗
PubMed1998

The design principles of axilla deodorant fragrances.

There are a number of ways that deodorant products control malodor: a) by suppressing sweat, b) by inhibiting bacterial activity, and c) by covering malodor. The paper focuses on the Givaudan Roure methodology used to develop fragrances that effectively cover malodor. Several steps are involved in the development of a successful deodorant fragrance. First, we test for substantivity of the deodorant fragrance material in the axilla, using odor value technology. Second, using an in vitro test with reconstituted axilla odor, we determine the effectiveness of the substantive fragrance material with carefully screened panelists. Third, using a multichannel olfactive blender, the perfumer creates a fragrance heart with effective deodorant fragrance materials that cover malodor in the vapor phase. Finally, the hedonically pleasing heart is used to create the final fragrance, which is then optimized using our in vitro test method.

Deodorants↗
PubMed1998

The time course of auditory perceptual learning: neurophysiological changes during speech-sound training.

Here we report that training-associated changes in neural activity can precede behavioral learning. This finding suggests that speech-sound learning occurs at a pre-attentive level which can be measured neurophysiologically (in the absence of a behavioral response) to assess the efficacy of training. Children with biologically based perceptual learning deficits as well as people who wear cochlear implants or hearing aids undergo various forms of auditory training. The effectiveness of auditory training can be difficult to assess using behavioral methods because these populations are communicatively impaired and may have attention and/or cognitive deficits. Based on our findings, if neurophysiological changes are seen during auditory training, then the training method is effectively altering the neural representation of the speech/sounds and changes in behavior are likely to follow.

Acoustic Stimulation↗
PubMed1998

Toxic epidermal necrolysis syndrome: mortality rate reduced with early referral to regional burn center.

Toxic epidermal necrolysis syndrome is an uncommon, acute, life-threatening disorder that involves sloughing of skin at the dermal-epidermal junction with associated mucositis. Between 1985 and 1995, 36 patients were treated for toxic epidermal necrolysis syndrome, at the Baltimore Regional Burn Center. A retrospective chart analysis was performed to discover significant determinants of mortality. Ninety-seven percent of the patients (35 of 36) were referred from outside institutions after an average of 6.3 +/- 0.8 days. Analysis of the data shows that patients who survived had been referred 7.5 days earlier than nonsurvivors (4.0 +/- 0.5 days versus 11.5 +/- 1.4 days, p < 0.001). When the patients were separated into two groups on the basis of time of referral, those referred "early" (< or = 7 days) had a mortality rate of 4 percent (1 of 24) versus 83 percent (10 of 12) for those referred "late" (> 7 days) (p < 0.001). Data were available from transferring institutions for 21 of the 36 patients. Analysis of the microbiologic data from these 21 patients revealed bacteremia, and subsequent death occurred in 100 percent (6 of 6) of the patients referred with positive cultures, whereas bacteremia developed in only 33 percent (5 of 15) of the patients referred with negative cultures, for a mortality rate of 7 percent (1 of 15). In addition, 86 percent (6 of 7) of the patients who were referred late (> 7 days) had positive cultures on referral. The current trend toward prolonged treatment in outside facilities before referral to a burn center is detrimental to the care of patients with toxic epidermal necrolysis syndrome. The overall rate of bacteremia, septicemia, and mortality is significantly reduced with early (< or = 7 days) referral to a regional burn center.

Adolescent↗
PubMed1997

Is it really a mismatch negativity? An assessment of methods for determining response validity in individual subjects.

Mismatch negativity (MMN) responses were collected from 86 normal school-age children in response to synthesized speech syllables, /wa/and two variants of /ba/. Waveform characteristics and statistical properties of the responses were analyzed across stimulus conditions in order to assess methods for determining response validity in individuals. Methods were compared using signal detection theory techniques. Criteria based on measurements of response area, onset latency, and duration were the best indicators of response validity. Also a promising indicator of validity was the interval of significance based on Z transformations determined by considering the variance of the underlying noise distribution. Correlations of individual responses with the grand average and integral calculations of the response negativity showed somewhat lower d' values. Statistical methods which utilized response subaverages were the poorest indicators of response validity. Likely the methods are limited primarily by the signal to noise ratio of the MMN compared to the underlying physiologic noise. Improvement of the signal to noise ratio remains a significant factor in the interpretation of MMN for individual subjects.

Acoustic Stimulation↗
PubMed1997

Central auditory system plasticity: generalization to novel stimuli following listening training.

Behavioral perceptual abilities and neurophysiologic changes observed after listening training can generalize to other stimuli not used in the training paradigm, thereby demonstrating behavioral "transfer of learning" and plasticity in underlying physiologic processes. Nine normal-hearing monolingual English-speaking adults were trained to identify a prevoiced labial stop sound (one that is not used phonemically in the English language). After training, the subjects were asked to discriminate and identify a prevoiced alveolar stop. Mismatch negativity cortical evoked responses (MMN) were recorded to both labial and alveolar stimuli before and after training. Behavioral performance and MMNs also were evaluated in an age-matched control group that did not receive training. Listening training improved the experimental group's ability to discriminate and identify an unfamiliar VOT contrast. That enhanced ability transferred from one place of articulation (labial) to another (alveolar). The behavioral training effects were reflected in the MMN, which showed an increase in duration and area when elicited by the training stimuli as well as a decrease in onset latency when elicited by the transfer stimuli. Interestingly, changes in the MMN were largest over the left hemisphere. The results demonstrate that training can generalize to listening situations beyond those used in training sessions, and that the preattentive central neurophysiology underlying perceptual learning are altered through auditory training.

Adolescent↗
PubMed1996

Auditory development reflected by middle latency response.

The auditory middle latency response (MLR) seems to have a relatively long developmental time course, extending through the first decade of life. Characteristics of each MLR component change developmentally not only with respect to waveform morphology but also with respect to response reliability, dependence on awareness state, and stimulus rate. Both human and animal studies indicate that these complex changes may be a result of multiple generating systems that show multiple time courses of development. This framework has practical ramifications in that clinical and research studies of MLR in young children must take into account the development sequence. Furthermore, it cannot be assumed a priori that research results obtained from adults will apply to young children. The complexity of the process raises intriguing questions regarding the functional development of auditory perception.

Animals↗
PubMed1996

Acoustic elements of speechlike stimuli are reflected in surface recorded responses over the guinea pig temporal lobe.

Auditory evoked potentials measured from the guinea pig temporal lobe surface reflect acoustic elements of synthesized speech syllables. Eliciting stimuli included a four formant anchor stimulus /ba/, with a 40-ms formant transition duration. The other stimuli differed from /ba/ along simple acoustic dimensions. The /pa/ stimuli differed on a VOT continuum; /da/ stimuli had a higher frequency F2 onset; /wa/ had a longer (80 ms) formant transition duration; and /bi/ differed in three vowel formant frequencies. The /ba/ and /da/ onset response latencies decreased systematically with increasing F2 onset frequency. The response to the /pa/ voicing increased in latency with increasing VOT and showed a physiologic discontinuity at VOT of 15-20 ms. Responses to /ba/ and /wa/ showed similar onset morphology but significant amplitude differences at latencies corresponding to vowel onset. Significant amplitude differences in /ba/ and /bi/ responses corresponded in latency to both consonant and vowel portions of the syllables. Similar to previous reports in the awake monkey for VOT, these results demonstrate in the anesthetized guinea pig that acoustic elements essential to speech perception are reflected in aggregate response of ensembles of cortical neurons.

Animals↗
PubMed1996

Human alveolar capillaries undergo angiogenesis in pulmonary veno-occlusive disease.

The bronchial circulation undergoes angiogenesis in several pathological conditions, such as lung neoplasm and bronchiectasis, but whether the pulmonary circulation can do this has been questioned. A woman treated with mitomycin C and 5-fluorouracil developed progressive, fatal pulmonary hypertension over 5 months. In addition to light and transmission electron microscopic examination of her lung, her pulmonary vasculature was cast and the casts were studied with scanning electron microscopy. Light microscopy showed that she had pulmonary veno-occlusive disease and angiomatoid capillary growth in the alveolar walls. Transmission electron microscopy confirmed the presence of pulmonary hypertension and showed thickened endothelial basement membrane. Scanning electron microscopy of the cast blood vessels showed distortion and destruction of alveolar capillaries prohibiting the passage of erythrocytes. Large new capillaries developed on top of, and were connected to, the shrivelled capillaries that made up the alveolar wall. The new capillaries were larger and fewer, which reduced the alveolar-capillary interface. Arteries and veins were irregularly narrowed and the veins had broad muscularity. Oedema was present, and the pulmonary lymphatics were extensively cast, especially in the lobular septa, but the lymphatics had a normal appearance. It appears that this patient suffered extensive capillary damage and venous occlusion and that the response was extensive new capillary formation, sometimes in angiomatoid configurations, and hypertrophy of pulmonary veins and arteries. Casting the microvasculature and viewing it with scanning electron microscopy identified new alveolar capillaries in this patient with acquired pulmonary hypertension.

Adult↗
PubMed1995

Thyrotropin-releasing hormone: does two hundred micrograms provide effective stimulation to the preterm fetal pituitary gland compared with four hundred micrograms?

OBJECTIVE: Our purpose was to compare the response of the fetal pituitary-thyroid axis to 200 and 400 micrograms of thyrotropin-releasing hormone administered to the mother immediately before delivery with a control group. STUDY DESIGN: A randomized controlled trial was conducted of 26 women at gestational ages between 24 weeks and 33 weeks 6 days who had received one or more doses of betamethasone who were expected to be delivered within 1 to 4 hours. Women received either 200 or 400 micrograms of thyrotropin-releasing hormone or were in the control group. RESULTS: Thyroid-stimulating hormone determinations on cord blood had a higher mean level in both treatment groups compared with the control group. No differences were seen in cord blood results between the two treatment groups for thyroid-stimulating hormone, thyroxine, triiodothyronine, free thyroxine, free triiodothyronine, and prolactin levels. The only other differences found were in a higher level in total thyroxine and a lower level of free thyroxine in the 400 micrograms thyrotropin-releasing hormone group compared with the 200 micrograms group in the 48-hour blood determinations. CONCLUSION: Both 200 and 400 micrograms of thyrotropin-releasing hormone provided fetal pituitary stimulation, as reflected in fetal thyroid-stimulating hormone levels in cord blood, and both gave significantly higher levels compared with a control group.

Adult↗
PubMed1995

Acoustic features and acoustic changes are represented by different central pathways.

The central processing of acoustic stimulus changes can be observed neurophysiologically in the mismatch negativity auditory evoked potential (MMN). Stimuli differing in interaural phase were used to investigate the contributions of the primary and non-primary auditory pathways to the encoding of binaural stimuli and to investigate passively elicited measures of binaural processing in experimental animals. In guinea pigs, the MMN was obtained in response to 1000 Hz tones embedded in white noise (S:N = 2 dB). Using a modified oddball paradigm (that is, two stimuli presented in a series, each with a different probability of occurrence), stimuli were presented binaurally with both the tone and noise in-phase to the two ears (S0N0) as the standard stimulus ans the tone 180 degrees out-of-phase (S(PI)N0) as the deviant stimulus. The MMN, by definition, should occur only in response to a change, or 'mismatch,' between the standard and deviant stimuli. The response to the deviant stimulus in the oddball paradigm was compared to the response to the same stimulus when presented in a series alone. The responses to S0N0 and S(PI)N0 collected in a series alone, termed the intrinsic responses, were also compared. Responses were recorded from two surface epidural electrodes - one at the posterior midline and one over the left temporal lobe. AEPs from these locations have been shown to reflect the activity of primary and non-primary thalamo-cortical pathways respectively. A significant MMN was observed at the midline electrode, but no MMN was observed over the temporal lobe.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1995

Neurophysiologic bases of speech discrimination.

The mismatch negativity (MMN) is an automatic cortical evoked potential that signifies the brain's detection of acoustic change. In other words, the MMN reflects the neurophysiologic processes that underlie auditory discrimination. As such, the MMN provides an objective tool for evaluating central auditory mechanisms involved in speech perception. We are using the MMN to study the central auditory processes that encode acoustic changes important for speech perception in 1) normal-hearing adults and children, 2) individuals with impaired auditory systems (including persons with learning disabilities, attention deficit disorders, cochlear implants), and 3) an animal model. Specifically, we have demonstrated that the MMN provides information about the central processing of fine acoustic differences, the neuroanatomic pathways that encode acoustic change, central auditory processing in the presence of peripheral hearing deficits, and central auditory system plasticity. In addition, we have considered methodological challenges associated with measuring the MMN in individual subjects. Several methodological issues--including appropriate stimuli, stimulus presentation variables, the recording protocol and environment, and validation of the MMN in individuals--are discussed.

Child↗
PubMed1995

The middle latency response generating system.

In summary, primary pathways are specifically auditory-sensitive, show fine frequency tuning, and good time-locking. The responses are reliable and show substantial binaural interactions. The primary pathway includes the ventral portion of the medial geniculate and the primary auditory cortex. The animal MLR recorded from over the temporal lobe, the temporal response, has been associated with the primary pathway because it is affected by pharmacological inactivation of MGv and electrolytic lesions of the primary auditory cortex. It is a large, reliable, rate-sensitive response, that shows a relatively late development and high degree of binaural interaction. Non-primary pathways are multimodal, broadly tuned, and show only mild binaural interaction. The midline response is associated with the non-primary areas because it is affected by pharmacologic inactivation of MGcm and mRF, but is not affected by inactivation of MGv or lesions of auditory cortex. The midline response is relatively small, labile, and rate-resistant. It develops early and shows only a small degree of binaural interaction. The generation of MLR thus appears to reflect an interplay of primary and non-primary areas in the auditory thalamo-cortical pathway. The non-primary and primary components may be differentiated in numerous ways: by lesions, by stimulus variations, and topographically. The non-primary components appear to develop early and are probably sleep state dependent, while the primary components develop later and are reliable even in sleep. In young children, it is essential to monitor sleep state in order to obtain reliable recordings, leading us to speculate that the non-primary components dominate the MLR.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1994

Binaural response patterns in subdivisions of the medial geniculate body.

Auditory evoked potentials (AEPs) to binaural click stimulation were examined in the ventral (MGv) and caudomedial (MGcm) subdivisions of the medial geniculate body (MG) in guinea pigs. Binaural stimulation caused a decrease in amplitude for the response component recorded from the MGv, but an increase in amplitude for the AEP component recorded from the MGcm. Findings suggest that the evoked responses recorded from MGv and MGcm are functionally distinct. The inhibitory binaural response (BR) pattern seen in MGv was similar to that of the middle latency response (MLR) component recorded over the temporal cortex, while the additive BR pattern typical of the MGcm was similar to that of the surface midline MLR component. Furthermore, these data imply that the binaural response patterns seen in the primary and non-primary auditory cortex may be processed and encoded at the thalamic level. It is concluded that the distinct BR patterns noted for the two MG subdivisions reflect the predominant type of binaurally responsive neurons within the respective pathways.

Acoustic Stimulation↗
PubMed1994

Discrimination of speech-like contrasts in the auditory thalamus and cortex.

The neurophysiologic discrimination of acoustic contrasts was investigated as reflected by the mismatch negativity (MMN) response. Evoked responses were recorded from guinea pig thalamus (medial geniculate nucleus) and epidural surface in response to synthesized speech contrasts /ga/-/da/ and /ba/-/wa/. From the caudomedial portion of the medial geniculate nucleus, /ba/-/wa/ elicited a strong mismatch response, whereas /ga/-/da/ did not. Neither stimulus contrast elicited an MMN from the ventral, or primary, portion of medial geniculate. Both stimulus contrasts elicited an MMN from the midline surface. Neither contrast elicited an MMN from the surface over the temporal lobe. Results indicate a hierarchy of processing of the spectrotemporal changes which characterize formant transitions. Also, results indicate that the nonprimary portions of the auditory pathway contribute substantially to the MMN.

Animals↗