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Biomedical subjects

C Lorenzi

Publications and source records attributed to C Lorenzi.

43 records · Page 3Linked to original sources
PubMed1997

Modulation masking in listeners with sensorineural hearing loss.

This study compares amplitude-modulation (AM) masking in listeners with normal hearing and in listeners with a hearing loss. To address this issue, we measured the detection of sinusoidal AM applied to a white noise carrier, as a function of the frequency of a masking sinusoidal AM applied to the same noise carrier. These input filter patterns were measured for four listeners with normal hearing and three listeners with moderate or mild-to-severe sensorineural hearing losses. Stimuli were presented at 50 dB SL for all listeners with normal hearing and for two of the three listeners with hearing loss. The third listener with hearing loss was tested at 25 dB SL. For the listeners with normal hearing, the input filter patterns obtained for 100-Hz signal modulation had a broad bandpass characteristic. All input filter patterns showed a primary masking peak at 100 Hz. A secondary masking peak was apparent also at 50 Hz. For the listeners with impaired hearing, the unmasked modulation thresholds were similar to those measured in the listeners with normal hearing. One listener with a moderate hearing loss exhibited a broadly tuned input filter pattern with a masking peak at 100 Hz, but no secondary peak. The two other listeners with moderate or mild-to-severe sensorineural hearing loss showed no main masking peak and increased thresholds at low masker modulation frequencies. These results suggest that cochlear damage may affect performance in a modulation masking task.

Adult↗
PubMed1997

Discrimination of temporal asymmetry in cochlear implantees.

Several studies have recently demonstrated that normal-hearing listeners are sensitive to short-term temporal asymmetry in the envelopes of sinusoidal or noise carriers. This paper presents a study in which cochlear implantees were presented trains of current pulses with temporally asymmetric envelopes through one channel of an implant that stimulates the auditory nerve directly, thereby bypassing cochlear processes. When the level of the stimuli was adjusted to fit their audibility range, the implantees were able to discriminate temporal asymmetry over a much wider range than normal-hearing listeners. The results suggest that the perception of temporal asymmetry is limited by compression in the normal cochlea.

Adult↗
PubMed1995

Neuronal correlates of perceptual amplitude-modulation detection.

The goal of the present paper is to relate the coding of amplitude modulation (AM) in the auditory pathway to the behavioral detection performance. To address this issue, the detectability of AM was estimated by modelling a single neuron located in the central nucleus of the inferior colliculus (IC). The computational model is based on cochlear nucleus responses and a coincidence detection mechanism. The model replicated the main feature of the neuronal AM transfer function, namely a bandpass function. The IC-unit model was initially tuned to a 200-Hz modulation frequency. A single neurometric function for AM detection at this modulation frequency was generated using a 2-interval, 2-alternative forced-choice paradigm. On each trial of the experiments, AM was taken to be correctly detected by the model if the number of spikes in response to the modulated signal exceeded the number of spikes in an otherwise identical interval that contained an unmodulated signal. Psychometric functions for 4 human subjects were also measured under the same stimulus conditions. Comparison of the simulated neurometric and psychometric functions suggested that there was sufficient information in the rate response of an IC neuron well-tuned in the modulation-frequency domain to support behavioral detection performance.

Acoustic Stimulation↗
PubMedDate not supplied

Serotonin receptor 2A, 2C, 1A genes and response to lithium prophylaxis in mood disorders.

The aim of this study was to investigate the influence of serotonin receptors 2A, 2C and 1A gene variants on lithium prophylactic efficacy in mood disorders. One hundred and twenty-four subjects affected by bipolar (n=102) and major depressive (n=22) disorder were followed prospectively for an average of 52 months and were typed for 5-HT2A (T102C: n=111, HTP: n=104), 5-HT2C (n=110) and 5-HT1A (n=61) variants. Both 5-HT2A and 5-HT2C variants were not associated with lithium outcome. Consideration of possible stratification effects like gender, polarity, family history, age at onset and duration of lithium treatment did not influence results. No 5-HT1A gene variant was identified. 5-HT2A and 2C variants are not, therefore, associated with lithium prophylactic efficacy in mood disorders.

Adult↗
PubMedDate not supplied

Influence of 5-HTTLPR and TPH variants on illness time course in mood disorders.

The aim of our study was to investigate gene variants in the long-term outcome of mood disorders. We retrospectively studied a sample of inpatients affected by recurrent and rapid cycling mood disorders. The serotonin transporter gene-linked functional polymorphic region (5-HTTLPR) and the A218C tryptophan hydroxylase (TPH) gene variant were determined using a PCR-based technique. For 5-HTTLPR polymorphism we genotyped 435 inpatients affected by major depressive (n=153), bipolar (n=213) and rapid cycling (n=69) mood disorders and 456 controls; for TPH we genotyped 399 inpatients (MD, n=132; BP, n=203; rapid cycling n=64) and 259 controls. Random Regression Model analysis was used to investigate the longitudinal time course of the illness. 5-HTTLPR and TPH polymorphisms were not associated with mood disorders time course. However we observed an excess of 5-HTTLPR*long alleles among rapid cycling subjects compared to both controls (P=0.018) and remitting mood disorders (P=0.006). TPH frequencies did not differ between mood disorders subtypes. Our results suggest that 5-HTTLPR variants may confer a susceptibility toward rapid cycling mood disorders.

Adult↗
PubMedDate not supplied

Tryptophan hydroxylase gene and response to lithium prophylaxis in mood disorders.

Lithium is an effective prophylactic agent in mood disorders but not all patients with mood disorders respond to lithium therapy; it is therefore necessary to identify responders prior to treatment. Clinical predictors account for about half of the variance and it is probable that genetic factors play a substantial role. The aim of this study was to investigate the possible association between the tryptophan hydroxylase (TPH) gene and prophylactic efficacy of lithium in mood disorders. One hundred and eight subjects affected by bipolar (n = 90) and major depressive (n = 18) disorder were followed prospectively for an average of 50.4 months and were typed for their TPH variant using polymerase chain reaction techniques. TPH variants were marginally associated with lithium outcome (F = 3.16; d.f.=2,105; P = 0.046). Subjects with the TPH*A/A variant showed a trend toward a worse response compared to both TPH*A/C and TPH*C/C variants. Consideration of possible stratification effects such as gender, polarity or age at onset did not influence the observed association. TPH variants may be a possible factor influencing the prophylactic efficacy of lithium in mood disorders.

Adult↗