Hörverlust bei adulten Ratten führt zu kognitiver Verminderung der visuell-räumlichen Aufmerksamkeit und reduzierter Ultraschallvokalisation während sozialer Interaktion

Hearing loss in the elderly has been associated with difficulties in speech comprehension and cognitive decline. Not least, it is a possible risk factor for dementia. We already showed that hearing loss leads to reduced neuronal activity in the medial prefrontal cortex (mPFC). To investigate the impact on cognitive function and communication, we here tested adult rats in behavioral paradigms for motor activity, attention and impulse control, as well as social interaction, including ultrasonic vocalization (USV).

In a cohort of adult male Sprague Dawley rats, hearing loss was induced under anaesthesia with intracochlear injection of neomycin (n=11). Naive (n=10) and sham-operated rats (n=7) served as control. Hearing loss was verified after surgery with auditory brainstem response (ABR) measurement. Furthermore, the rats were tested for motor activity (Open Field) and social interaction before surgery and at week 1, 2, 4, 8, 16, and 24 after surgery. From week 8 onwards, the rats were tested in the Five Choices Serial Reaction Time Task (5CSRTT) for visuospatial attention, impulse control, learning, and memory. In this paradigm, rats have to react to a light stimulus in one of five holes of the aperture, which is shortened from session to session.

In the Open Field, deafened rats moved faster and a longer distance than the controls (both p<0.05). Social interaction was significantly less between cage mates in the deafened rats (p<0.05) and the count of USV was significantly reduced in deafened rats in week 4 (p<0.05). Learning the 5CSRTT was significantly impeded in the deafened group (p<0.05). Moreover, the accuracy, associated with attention, was reduced in deafened rats (p<0.05). Looking at the omission rate, the deafened rats seemed to be less likely to miss a trial (p<0.05). For training and retesting it is worth mentioning that the deafened rats had a significantly shorter latency between correct responding and getting the reward (p<0.05).

Hearing loss in adult rats leads to hyperlocomotion and less USV. Furthermore, these rats exhibit deficits in initial visuospatial attention as evidenced by a lower accuracy rate and delayed comprehension of the new task. These cognitive impairments may be associated to compromised neuronal activity in the mPFC, as shown in a prior publication. Therefore, this model could serve as a valuable tool for investigating the effect of neuromodulatory stimulation on cognitive decline attributed to hearing impairment.