The protective effects of nutritional antioxidant therapy on Ehrlich solid tumor-bearing mice depend on the type of antioxidant therapy chosen: histology, genotoxicity and hematology evaluations.

Strong evidence indicates that reactive oxygen species (ROS) play an important role in the initiation as well as the promotion phase of carcinogenesis. Studies support the role of ROS in cancer, in part, by showing that dietary antioxidants act as cancer-preventive agents. Although results are promising, the research on this topic is still controversial. Thus, the aim of this study was to investigate whether vitamins C, E and pequi oil can, individually, provide prevention and/or be used afterward as an adjuvant in cancer therapy. Ehrlich solid tumor-bearing mice received antioxidant as follows: before tumor inoculation, before and after tumor inoculation (continuous administration), and after tumor inoculation; morphometric analyses of tumor, genotoxicity and hematology were then carried out. Antioxidant administrations before tumor inoculation effectively inhibited its growth in the three experimental protocols, but administrations after the tumor's appearance accelerated tumor growth and favored metastases. Continuous administration of pequi oil inhibited the tumor's growth, while the same protocol with vitamins E and C accelerated it, favoring metastasis and increasing oxidative stress on erythrocytes. Except for continuous administration with vitamin E, the development of ascites tumor metastases was linked with increased inflammation. Results suggest that the efficiency and applicability of antioxidants in the medical clinic can depend not only on the nature of the antioxidant, the type and stage of cancer being treated and the prevailing oxygen partial pressure in the tissues, but also on the type of antioxidant therapy chosen.

Hearing loss severity: impaired processing of formant transition duration.

Normal hearing listeners exploit the formant transition (FT) detection to identify place of articulation for stop consonants. Neuro-imaging studies revealed that short FT induced less cortical activation than long FT. To determine the ability of hearing impaired listeners to distinguish short and long formant transitions (FT) from vowels of the same duration, 84 mild to severe hearing impaired listeners and 5 normal hearing listeners were asked to detect 10 synthesized stimuli with long (200 ms) or short (40 ms) FT among 30 stimuli of the same duration without FT. Hearing impaired listeners were tested with and without hearing aids. The effect of the difficulty of the task (short/long FT) was analysed as a function of the hearing loss with and without hearing aids. Normal hearing listeners were able to detect every FT (short and long). For hearing impaired listeners, the detection of long FT was better than that of short ones irrespective of their degree of hearing loss. The use of hearing aids improved detection of both kinds of FT; however, the detection of long FT remained much better than the detection of the short ones. The length of FT modified the ability of hearing impaired patients to detect FT. Short FT had access to less cortical processing than long FT and cochlea damages enhanced this specific deficit in short FT brain processing. These findings help to understand the limit of deafness rehabilitation in the time domain and should be taken into account in future devices development.

Spectral and temporal processing in human auditory cortex.

We used positron emission tomography to examine the response of human auditory cortex to spectral and temporal variation. Volunteers listened to sequences derived from a standard stimulus, consisting of two pure tones separated by one octave alternating with a random duty cycle. In one series of five scans, spectral information (tone spacing) remained constant while speed of alternation was doubled at each level. In another five scans, speed was kept constant while the number of tones sampled within the octave was doubled at each level, resulting in increasingly fine frequency differences. Results indicated that (i) the core auditory cortex in both hemispheres responded to temporal variation, while the anterior superior temporal areas bilaterally responded to the spectral variation; and (ii) responses to the temporal features were weighted towards the left, while responses to the spectral features were weighted towards the right. These findings confirm the specialization of the left-hemisphere auditory cortex for rapid temporal processing, and indicate that core areas are especially involved in these processes. The results also indicate a complementary hemispheric specialization in right-hemisphere belt cortical areas for spectral processing. The data provide a unifying framework to explain hemispheric asymmetries in processing speech and tonal patterns. We propose that differences exist in the temporal and spectral resolution of corresponding fields in the two hemispheres, and that they may be related to anatomical hemispheric asymmetries in myelination and spacing of cortical columns.

A cortical region sensitive to auditory spectral motion.

The functional architecture of human auditory cortex is still poorly understood compared with that of visual cortex, yet anatomical and electrophysiological studies in non-human primates suggest that the auditory cortex also might be functionally specialized, in a model of parallel and hierarchical organization. In particular, spectral changes such as the formant transitions of speech, or spectral motion (SM) by analogy with visual motion, could be processed in specialized cortical regions. In this study, positron emission tomography (PET) was used to identify which auditory cortical region are involved in SM analysis. We found that a bilateral secondary auditory cortical region, located in the caudal-lateral belt of auditory cortex, was more sensitive to auditory stimuli containing spectral changes than to matched stimuli with a stationary spectral profile. This result suggests that analogies between sensory systems could prove useful in the research into the functional organization of the auditory cortex.

Voice-selective areas in human auditory cortex.

The human voice contains in its acoustic structure a wealth of information on the speaker's identity and emotional state which we perceive with remarkable ease and accuracy. Although the perception of speaker-related features of voice plays a major role in human communication, little is known about its neural basis. Here we show, using functional magnetic resonance imaging in human volunteers, that voice-selective regions can be found bilaterally along the upper bank of the superior temporal sulcus (STS). These regions showed greater neuronal activity when subjects listened passively to vocal sounds, whether speech or non-speech, than to non-vocal environmental sounds. Central STS regions also displayed a high degree of selectivity by responding significantly more to vocal sounds than to matched control stimuli, including scrambled voices and amplitude-modulated noise. Moreover, their response to stimuli degraded by frequency filtering paralleled the subjects' behavioural performance in voice-perception tasks that used these stimuli. The voice-selective areas in the STS may represent the counterpart of the face-selective areas in human visual cortex; their existence sheds new light on the functional architecture of the human auditory cortex.

Event-related fMRI of the auditory cortex.

An event-related protocol was designed to permit auditory fMRI studies minimally affected by the echo-planar noise artifact; a long time interval (TR = 10 s) between each cerebral volume acquisition was combined with stroboscopic data acquisition, and event-related curves were reconstructed with a 1-s resolution. The cerebral hemodynamic-response time course to a target auditory stimulus was measured in five individual subjects using this method. Clear bell-shaped event-related responses were observed bilaterally in all individuals in primary auditory cortex (A1) as well as in laterally extending secondary cortical fields. Group-average event-related curves attained their maxima (0.5-0.7%) 3 s after stimulus onset in A1 (4 s for more anterior and lateral regions of auditory cortex), and signal had returned to near-baseline level 6 s after stimulus onset. The stroboscopic event-related method appeared effective in minimizing effects of the interaction between scanning noise and experimental auditory stimulation; it adds useful temporal information to the spatial resolution afforded by fMRI in studies of human auditory function, while allowing presentation of auditory stimuli on a silent background.

Lateralization of speech and auditory temporal processing.

To investigate the role of temporal processing in language lateralization, we monitored asymmetry of cerebral activation in human volunteers using positron emission tomography (PET). Subjects were scanned during passive auditory stimulation with nonverbal sounds containing rapid (40 msec) or extended (200 msec) frequency transitions. Bilateral symmetric activation was observed in the auditory cortex for slow frequency transitions. In contrast, left-biased asymmetry was observed in response to rapid frequency transitions due to reduced response of the right auditory cortex. These results provide direct evidence that auditory processing of rapid acoustic transitions is lateralized in the human brain. Such functional asymmetry in temporal processing is likely to contribute to language lateralization from the lowest levels of cortical processing.

Recovery from nonfluent aphasia after melodic intonation therapy: a PET study.

We examined mechanisms of recovery from aphasia in seven nonfluent aphasic patients, who were successfully treated with melodic intonation therapy (MIT) after a lengthy absence of spontaneous recovery. We measured changes in relative cerebral blood flow (CBF) with positron emission tomography (PET) during hearing and repetition of simple words, and during repetition of MIT-loaded words. Without MIT, language tasks abnormally activated right hemisphere regions, homotopic to those activated in the normal subject, and deactivated left hemisphere language zones. In contrast, repeating words with MIT reactivated Broca's area and the left prefrontal cortex, while deactivating the counterpart of Wernicke's area in the right hemisphere. The recovery process induced by MIT in these patients probably coincides with this reactivation of left prefrontal structures. In contrast, the right hemisphere regions abnormally activated during simple language tasks seem to be associated with the initial persistence of the aphasia. This study supports the idea that abnormal activation patterns in the lesioned brain are not necessarily related to the recovery process.