Behavioural evidence for enhanced olfactory and trigeminal perception in congenital hearing loss.

Sensory deprivation, especially hearing loss (HL), offers a valuable model for studying neuroplasticity in the human brain and adaptive behaviours that support the daily lives of those with limited or absent sensory input. The study of olfactory function is particularly important as it is an understudied aspect of sensory deprivation. This study aimed to compare the effects of congenital HL on olfactory capacity by using psychophysical tasks. Methodological concerns from previous studies regarding the onset of HL and cognitive assessments were addressed. We recruited 11 individuals with severe-to-profound sensorineural HL (SNHL) since birth and 11 age- and sex-matched typical hearing non-signers. We used standardized neuropsychological tests to assess typical cognition among participants with SNHL. We evaluated olfactory functions by assessing olfactory detection threshold, odour discrimination and odour identification. Hearing-impaired participants outperformed their typical hearing counterparts in olfactory tasks. We further evaluated the accuracy and response time in identifying and localizing odours to disentangle olfactory sensitivity from trigeminal system sensitivity. Participants with SNHL demonstrated higher sensitivity to both the identification and localization tasks. These findings suggest that congenital SNHL is associated with enhanced higher-level olfactory processing and increased trigeminal sensitivity.

Olfactory perception in patients with a mild traumatic brain injury: a longitudinal study.

OBJECTIVE: This longitudinal study aimed to evaluate olfactory perception in patients with first time mild traumatic brain injury (mTBI) 2-4 weeks (baseline) and 6 months (follow-up) following their trauma. METHODS: At baseline, we enrolled 107 participants (54 healthy controls; 53 patients with mTBI). Thirty-nine healthy controls and 32 patients with mTBI returned for follow-up. We assessed odor detection (yes/no paradigm) and odor perception with a self-reported evaluation of intensity and pleasantness of four common odorants, by using an olfactometer, i.e., a computer controlled automated odor presentation device. RESULTS: At baseline, patients with mTBI showed significantly more difficulty detecting odors; however, they perceived them as more intense and less pleasant. These effects vanished at follow-up. CONCLUSION: These results suggest that patients with mTBI suffer from altered olfactory detection and perception in the first weeks following their trauma. This may have an impact on eating behavior and quality of life. Further, our data suggest recovery of olfactory function within the first six months following a head trauma.

Verbal Episodic Memory Alterations and Hippocampal Atrophy in Acute Mild Traumatic Brain Injury.

Episodic memory deficit is a symptom frequently observed after a mild traumatic brain injury (mTBI). However, few studies have investigated the impact of a single and acute mTBI on episodic memory and structural cerebral changes. To do so, we conducted two experiments. In the first, we evaluated verbal episodic memory by using a word recall test, in 52 patients with mTBI (mean age 33.1 [12.2] years) 2-4 weeks after a first mTBI, compared with 54 healthy controls (31.3 [9.2] years) and followed both groups up for 6 months. In the second, we measured hippocampal volume in a subset of 40 participants (20 patients with mTBI, 20 controls) from Experiment 1 using magnetic resonance imaging (MRI; T1-weighted images) and correlated memory performance scores to hippocampal volume. Experiment 1 showed significantly reduced verbal episodic memory within the first month after an mTBI and a tendency for a reduction 6 months later, more pronounced for men. In Experiment 2, patients with mTBI exhibited a generally reduced hippocampal volume; however, we did not observe any linear correlation between hippocampal volume and memory scores. These results suggest that one single mTBI is associated with both episodic memory alteration and reduced volume of the hippocampus in the acute phase. Future studies are needed to elucidate the link between both measures.

Early parosmia signs and affective states predicts depression and anxiety symptoms six months after a mild Traumatic Brain Injury.

This longitudinal study aimed to evaluate qualitative (parosmia) and quantitative (hyposmia/anosmia) olfaction 2-4 weeks (baseline) and six months (follow-up) after a mild traumatic brain injury (mTBI). We further evaluated the predictive value of baseline depression, anxiety and olfaction scores on depression and anxiety at follow-up. At baseline, olfactory function and affective state were assessed in 107 participants (53 patients with mild TBI; 54 healthy controls). At follow-up, data were collected on 71 participants (32 patients, 39 controls). Both at baseline and follow-up, patients with mild TBI showed more signs of parosmia, depression and anxiety, compared to controls. However, patients did not, neither at baseline nor follow-up, show quantitative olfactory impairment. Moreover, while baseline scores of depression and anxiety helped predict the development of symptoms of depression and anxiety at follow up, adding parosmia scores to the prediction model significantly increased the amount of explained variances. Clinicians should implement affective and olfactory evaluation to predict patients' affective outcome.

Visual memory performance following mild traumatic brain injury and its relationship with intellectual functioning.

To compare the visual memory performance of uncomplicated and complicated mild TBI (mTBI) groups with that of a control group on the Rey Complex Figure Test (RCFT). We also aimed to explore the influence of factors such as age, gender, education, occupation, and intellectual functioning on visual memory in individuals with mTBI. The RCFT and the Wechsler Abbreviated Scale of Intelligence (WASI-II) were administered to 138 participants (90 uncomplicated mTBI patients, 19 complicated mTBI patients, and 29 controls). The mTBI patients demonstrated significantly lower scores than control participants on both immediate and delayed RCFT recall conditions, with performance in the low average and borderline range. However, there was no difference in performance between the two mTBI groups on the recall conditions. In addition, no significant differences were observed across the three groups on the recognition condition. The WASI-II Performance and Verbal IQ scales explained most of the variance in the immediate and delayed RCFT recall conditions but were not associated with performance on the recognition condition. In contrast with the recognition processes involved in visual memory, recall processes seem to be more vulnerable following mTBI and both verbal and performance IQ seem to be related to visual memory performance.

Olfactory, cognitive and affective dysfunction assessed 24 hours and one year after a mild Traumatic Brain Injury (mTBI).

Objective: This cross-sectional study aimed to evaluate olfaction 24 h (baseline) and 1 year (follow-up) after a mild traumatic brain injury (TBI). We further evaluated the influence of the cognition and affective state on olfactory function. Method: At baseline, olfactory function, neuropsychological, and affective states were assessed in 42 patients (20 mild TBI; 22 orthopedic injury). At follow-up, 12 patients with mild TBI and 7 controls could be included, and we assessed olfactory function, affective states, and post-concussion symptoms. Results: At baseline, patients with mild TBI demonstrated significantly reduced olfactory function, compared to controls, with more than 55% of the patients presenting signs of hyposmia. One year later, no significant differences in olfactory scores between cases and controls were observed. However, patients with mild TBI who had exhibited hyposmia at baseline exhibited significantly higher anxiety levels and more post-concussion symptoms than patients with mild TBI with normal olfactory function at baseline. Conclusions: In the acute phase of mild TBI a majority of patients has impaired olfactory function. Further patients with olfactory dysfunction are more likely to exhibit post-concussion and anxious symptoms at follow-up. Olfactory testing in the acute phase may therefore serve as a screening tool for long-term outcome.

Boc Acts via Numb as a Shh-Dependent Endocytic Platform for Ptch1 Internalization and Shh-Mediated Axon Guidance.

During development, Shh attracts commissural axons toward the floor plate through a non-canonical, transcription-independent signaling pathway that requires the receptor Boc. Here, we find that Shh induces Boc internalization into early endosomes and that endocytosis is required for Shh-mediated growth-cone turning. Numb, an endocytic adaptor, binds to Boc and is required for Boc internalization, Shh-mediated growth-cone turning in vitro, and commissural axon guidance in vivo. Similar to Boc, Ptch1 is also internalized by Shh in a Numb-dependent manner; however, the binding of Shh to Ptch1 alone is not sufficient to induce Ptch1 internalization nor growth-cone turning. Therefore, the binding of Shh to Boc is required for Ptch1 internalization and growth-cone turning. Our data support a model where Boc endocytosis via Numb is required for Ptch1 internalization and Shh signaling in axon guidance. Thus, Boc acts as a Shh-dependent endocytic platform gating Ptch1 internalization and Shh signaling.