The functional anatomy of semantic retrieval is influenced by gender, menstrual cycle, and sex hormones.

This study examines the neurobiology of semantic retrieval and describes the influence of gender, menstrual cycle, and sex hormones on semantic networks. Healthy right-handed subjects (12 men, 12 women) were investigated with 3T-fMRI during synonym generation. Behavioral performance and sex hormone levels were assessed. Women were examined during the early follicular and midluteal cycle phase. The activation pattern in all groups involved left frontal and temporal as well as bilateral medial frontal, cingulate, occipital, basal ganglia, and cerebellar regions. Men showed greater left frontal activation than women in both menstrual cycle phases. Women yielded high correlations of left prefrontal activation with estradiol in the midluteal phase and with progesterone in both phases. Testosterone levels correlated highly with left prefrontal activation in all three groups. In all, we describe a cerebral network involved in semantic processing and demonstrate that it is significantly affected by gender and sex steroid hormones.

Functional anatomy of visuo-spatial working memory during mental rotation is influenced by sex, menstrual cycle, and sex steroid hormones.

Recent observations indicate that sex and level of steroid hormones may influence cortical networks associated with specific cognitive functions, in particular visuo-spatial abilities. The present study probed the influence of sex, menstrual cycle, and sex steroid hormones on 3D mental rotation and brain function using 3-T fMRI. Twelve healthy women and 12 men were investigated. Menstrual cycle and hormone levels were assessed. The early follicular and midluteal phase of the menstrual cycle were chosen to examine short-term cyclical changes. Parietal and frontal areas were activated during mental rotation in both sexes. Significant differences between men and women were revealed in both phases of menstrual cycle. In men we observed a significant correlation of activation levels with testosterone levels in the left parietal lobe (BA 40). In women, a cycle-dependent correlation pattern was observed for testosterone: brain activation correlated with this male hormone only during the early follicular phase. In both cycle phases females' brain activation was significantly correlated with estradiol in frontal and parietal areas. Our study provides evidence that fMRI-related activity during performance of cognitive tasks varies across sex and phases of the menstrual cycle. The variation might be partly explained by better task performance in men, but our results indicate that further explanations like basic neuronal or neurovascular effects modulated by steroid hormones must be considered. Both estradiol and testosterone levels may influence fMRI signals of cognitive tasks, which should affect selection of subjects for future fMRI studies.

Expression of BDNF and TrkB mRNAs in the crista neurosensory epithelium and vestibular ganglia following ototoxic damage.

Following ototoxic lesion with the aminoglycoside gentamicin, the vestibular neurosensory epithelia undergo degeneration and then limited spontaneous regeneration. The spatio-temporal expression of brain-derived neurotrophic factor (BDNF) and of its high affinity receptor (trkB) mRNA was investigated in the vestibular end organs and ganglia of chinchillas following gentamicin ototoxicity. In the vestibular ganglia of untreated chinchillas, the level of expression of BDNF mRNA is low. At 1 and 2 weeks after intraotic treatment with gentamicin, BDNF mRNA levels in the vestibular ganglia were elevated significantly compared to untreated chinchillas and chinchillas 4 weeks after treatment. At 4 weeks after gentamicin treatment, BDNF mRNA levels were at intact levels of expression. In the crista ampullaris, high levels of BDNF transcripts were found in the untreated chinchillas. At 1 and 2 weeks after treatment, when only supporting cells are present in the crista, BDNF mRNA was undetectable. Four weeks after aminoglycoside treatment BDNF mRNA was present in the epithelium but at lower levels than in the intact epithelium. In contrast to its ligand, high levels of trkB mRNA hybridization were present in the vestibular ganglia of untreated chinchillas and trkB mRNA levels did not change following gentamicin treatment. In the vestibular epithelia, trkB mRNA was not detected either in the intact epithelium or after gentamicin ototoxicity. These data suggest that BDNF may be involved in the maintenance of the vestibular ganglia and contribute to neurite outgrowth to new and repaired hair cells following ototoxic damage.

Cross-innervation of the thyroarytenoid muscle by a branch from the external division of the superior laryngeal nerve.

The neuroanatomy of the larynx was explored in seven dogs to assess whether there is motor innervation to the thyroarytenoid (TA) muscle from the external division of the superior laryngeal nerve (ExSLN). In 3 animals, such innervation was identified. Electrical stimulation of microelectrodes applied to the ExSLN resulted in contraction of the TA muscle, indicating that this nerve is motor in function. This was confirmed by electromyographic recordings from the TA muscle. Videolaryngostroboscopy revealed improvement in vocal fold vibration following stimulation of the ExSLN compared to without it. Previously, the TA muscle was thought to be innervated solely by the recurrent laryngeal nerve. This additional pathway from the ExSLN to the TA muscle may have important clinical implications in the treatment of neurologic laryngeal disorders such as adductor spasmodic dysphonia.

Function of the interarytenoid muscle in a canine laryngeal model.

The interarytenoid (IA) muscle has rarely been studied in the living larynx. In this work, the role of the IA muscle in phonation was studied in three dogs by means of an in vivo phonation model. The isolated action of the IA muscle was studied by sectioning and stimulating its nerve branch. As IA activity increased, subglottic pressure increased significantly until a plateau was reached. In the absence of superior laryngeal nerve stimulation, the fundamental frequency rose with increasing IA activity. In the presence of superior laryngeal nerve stimulation, however, no significant change in fundamental frequency was observed with increasing IA activity. Measurement of adductory force demonstrated that the IA muscle adducts primarily the posterior vocal fold. In this canine model, phonation was not possible without IA stimulation, owing to a large posterior glottic chink.