A pilot investigation of audiovisual processing and multisensory integration in patients with inherited retinal dystrophies

A Pilot Investigation of Visual Pathways in Patients with Mild Traumatic Brain Injury

In this study, we examined visual processing within primary visual areas (V1) in normal and visually impaired individuals who exhibit significant visual symptomology due to sports-related mild traumatic brain injury (mTBI). Five spatial frequency stimuli were applied to the right, left and both eyes in order to assess the visual processing of patients with sports-related mild traumatic brain injuries who exhibited visual abnormalities, i.e., photophobia, blurriness, etc., and controls. The measurement of the left/right eye and binocular integration was accomplished via the quantification of the spectral power and visual event-related potentials. The principal results have shown that the power spectral density (PSD) measurements display a distinct loss in the alpha band-width range, which corresponded to more instances of medium-sized receptive field loss. Medium-size receptive field loss may correspond to parvocellular (p-cell) processing deprecation. Our major conclusion provides a new measurement, using PSD analysis to assess mTBI conditions from primary V1 areas. The statistical analysis demonstrated significant differences between the mTBI and control cohort in the Visual Evoked Potentials (VEP) amplitude responses and PSD measurements. Additionally, the PSD measurements were able to assess the improvement in the mTBI primary visual areas over time through rehabilitation.

Vestibular Stimulation May Drive Multisensory Processing: Principles for Targeted Sensorimotor Therapy (TSMT)

At birth, the vestibular system is fully mature, whilst higher order sensory processing is yet to develop in the full-term neonate. The current paper lays out a theoretical framework to account for the role vestibular stimulation may have driving multisensory and sensorimotor integration. Accordingly, vestibular stimulation, by activating the parieto-insular vestibular cortex, and/or the posterior parietal cortex may provide the cortical input for multisensory neurons in the superior colliculus that is needed for multisensory processing. Furthermore, we propose that motor development, by inducing change of reference frames, may shape the receptive field of multisensory neurons. This, by leading to lack of spatial contingency between formally contingent stimuli, may cause degradation of prior motor responses. Additionally, we offer a testable hypothesis explaining the beneficial effect of sensory integration therapies regarding attentional processes. Key concepts of a sensorimotor integration therapy (e.g., targeted sensorimotor therapy (TSMT)) are also put into a neurological context. TSMT utilizes specific tools and instruments. It is administered in 8-weeks long successive treatment regimens, each gradually increasing vestibular and postural stimulation, so sensory-motor integration is facilitated, and muscle strength is increased. Empirically TSMT is indicated for various diseases. Theoretical foundations of this sensorimotor therapy are discussed.

Auditory and olfactory findings in patients with USH2A-related retinal degeneration-Findings at baseline from the rate of progression in USH2A-related retinal degeneration natural history study (RUSH2A)

Sensorineural hearing loss (SNHL) is characteristic of Usher syndrome type 2 (USH2), but less is known about SNHL in nonsyndromic autosomal recessive retinitis pigmentosa (ARRP) and olfaction in USH2A-associated retinal degeneration. The Rate of Progression of USH2A-related Retinal Degeneration (RUSH2A) is a natural history study that enrolled 127 participants, 80 with USH2 and 47 with ARRP. Hearing was measured by pure-tone thresholds and word recognition scores, and olfaction by the University of Pennsylvania Smell Identification Test (UPSIT). SNHL was moderate in 72% of USH2 participants and severe or profound in 25%, while 9% of ARRP participants had moderate adult-onset SNHL. Pure-tone thresholds worsened with age in ARRP but not in USH2 participants. The degree of SNHL was not associated with other participant characteristics in either USH2 or ARRP. Median pure-tone thresholds in ARRP participants were significantly higher than the normative population (p < 0.001). Among 14 USH2 participants reporting newborn hearing screening results, 7 reported passing. Among RUSH2A participants, 7% had mild microsmia and 5% had moderate or severe microsmia. Their mean (±SD) UPSIT score was 35 (±3), similar to healthy controls (34 [±3]; p = 0.39). Olfaction differed by country (p = 0.02), but was not significantly associated with clinical diagnosis, age, gender, race/ethnicity, smoking status, visual measures, or hearing. Hearing loss in USH2A-related USH2 did not progress with age. ARRP patients had higher pure-tone thresholds than normal. Newborn hearing screening did not identify all USH2A-related hearing loss. Olfaction was not significantly worse than normal in participants with USH2A-related retinal degeneration.

Partial recovery of visual function in a blind patient after optogenetic therapy

Optogenetics may enable mutation-independent, circuit-specific restoration of neuronal function in neurological diseases. Retinitis pigmentosa is a neurodegenerative eye disease where loss of photoreceptors can lead to complete blindness. In a blind patient, we combined intraocular injection of an adeno-associated viral vector encoding ChrimsonR with light stimulation via engineered goggles. The goggles detect local changes in light intensity and project corresponding light pulses onto the retina in real time to activate optogenetically transduced retinal ganglion cells. The patient perceived, located, counted and touched different objects using the vector-treated eye alone while wearing the goggles. During visual perception, multichannel electroencephalographic recordings revealed object-related activity above the visual cortex. The patient could not visually detect any objects before injection with or without the goggles or after injection without the goggles. This is the first reported case of partial functional recovery in a neurodegenerative disease after optogenetic therapy.

BBSome Component BBS5 Is Required for Cone Photoreceptor Protein Trafficking and Outer Segment Maintenance

Purpose

To identify the role of the BBSome protein Bardet-Biedl syndrome 5 (BBS5) in photoreceptor function, protein trafficking, and structure using a congenital mutant mouse model.

Methods

Bbs5-/- mice (2 and 9 months old) were used to assess retinal function and morphology. Hematoxylin and eosin staining of retinal sections was performed to visualize histology. Electroretinography was used to analyze rod and cone photoreceptor function. Retinal protein localization was visualized using immunofluorescence (IF) within retinal cryosections. TUNEL staining was used to quantify cell death. Transmission electron microscopy (TEM) was used to examine retinal ultrastructure.

Results

In the Bbs5-/- retina, there was a significant loss of nuclei in the outer nuclear layer accompanied by an increase in cell death. Through electroretinography, Bbs5-/- mice showed complete loss of cone photoreceptor function. IF revealed mislocalization of the cone-specific proteins M- and S-opsins, arrestin-4, CNGA3, and GNAT2, as well as a light-dependent arrestin-1 mislocalization, although perpherin-2 was properly localized. TEM revealed abnormal outer segment disk orientation in Bbs5-/-.

Conclusions

Collectively, these data suggest that, although BBS5 is a core BBSome component expressed in all ciliated cells, its role within the retina mediates specific photoreceptor protein cargo transport. In the absence of BBS5, cone-specific protein mislocalization and a loss of cone photoreceptor function occur.

Frontal cortex selectively overrides auditory processing to bias perception for looming sonic motion

Rising intensity sounds signal approaching objects traveling toward an observer. A variety of species preferentially respond to looming over receding auditory motion, reflecting an evolutionary perceptual bias for recognizing approaching threats. We probed the neural origins of this stark perceptual anisotropy to reveal how the brain creates privilege for auditory looming events. While recording neural activity via electroencephalography (EEG), human listeners rapidly judged whether dynamic (intensity varying) tones were looming or receding in percept. Behaviorally, listeners responded faster to auditory looms confirming a perceptual bias for approaching signals. EEG source analysis revealed sensory activation localized to primary auditory cortex (PAC) and decision-related activity in prefrontal cortex (PFC) within 200 ms after sound onset followed by additional expansive PFC activation by 500 ms. Notably, early PFC (but not PAC) activity rapidly differentiated looming and receding stimuli and this effect roughly co-occurred with sound arrival in auditory cortex. Brain-behavior correlations revealed an association between PFC neural latencies and listeners' speed of sonic motion judgments. Directed functional connectivity revealed stronger information flow from PFC → PAC during looming vs. receding sounds. Our electrophysiological data reveal a critical, previously undocumented role of prefrontal cortex in judging dynamic sonic motion. Both faster neural bias and a functional override of obligatory sensory processing via selective, directional PFC signaling toward auditory system establish the perceptual privilege for approaching looming sounds.

Psychobiological Responses Reveal Audiovisual Noise Differentially Challenges Speech Recognition

OBJECTIVES

In noisy environments, listeners benefit from both hearing and seeing a talker, demonstrating audiovisual (AV) cues enhance speech-in-noise (SIN) recognition. Here, we examined the relative contribution of auditory and visual cues to SIN perception and the strategies used by listeners to decipher speech in noise interference(s).

DESIGN

Normal-hearing listeners (n = 22) performed an open-set speech recognition task while viewing audiovisual TIMIT sentences presented under different combinations of signal degradation including visual (AVn), audio (AnV), or multimodal (AnVn) noise. Acoustic and visual noises were matched in physical signal-to-noise ratio. Eyetracking monitored participants' gaze to different parts of a talker's face during SIN perception.

RESULTS

As expected, behavioral performance for clean sentence recognition was better for A-only and AV compared to V-only speech. Similarly, with noise in the auditory channel (AnV and AnVn speech), performance was aided by the addition of visual cues of the talker regardless of whether the visual channel contained noise, confirming a multimodal benefit to SIN recognition. The addition of visual noise (AVn) obscuring the talker's face had little effect on speech recognition by itself. Listeners' eye gaze fixations were biased toward the eyes (decreased at the mouth) whenever the auditory channel was compromised. Fixating on the eyes was negatively associated with SIN recognition performance. Eye gazes on the mouth versus eyes of the face also depended on the gender of the talker.

CONCLUSIONS

Collectively, results suggest listeners (1) depend heavily on the auditory over visual channel when seeing and hearing speech and (2) alter their visual strategy from viewing the mouth to viewing the eyes of a talker with signal degradations, which negatively affects speech perception.

Acoustic noise and vision differentially warp the auditory categorization of speech

Speech perception requires grouping acoustic information into meaningful linguistic-phonetic units via categorical perception (CP). Beyond shrinking observers' perceptual space, CP might aid degraded speech perception if categories are more resistant to noise than surface acoustic features. Combining audiovisual (AV) cues also enhances speech recognition, particularly in noisy environments. This study investigated the degree to which visual cues from a talker (i.e., mouth movements) aid speech categorization amidst noise interference by measuring participants' identification of clear and noisy speech (0 dB signal-to-noise ratio) presented in auditory-only or combined AV modalities (i.e., A, A+noise, AV, AV+noise conditions). Auditory noise expectedly weakened (i.e., shallower identification slopes) and slowed speech categorization. Interestingly, additional viseme cues largely counteracted noise-related decrements in performance and stabilized classification speeds in both clear and noise conditions suggesting more precise acoustic-phonetic representations with multisensory information. Results are parsimoniously described under a signal detection theory framework and by a reduction (visual cues) and increase (noise) in the precision of perceptual object representation, which were not due to lapses of attention or guessing. Collectively, findings show that (i) mapping sounds to categories aids speech perception in "cocktail party" environments; (ii) visual cues help lattice formation of auditory-phonetic categories to enhance and refine speech identification.