Developmental Timing of Auditory Deprivation Influences Spatial Memory and Hippocampal Plasticity in Rats

Mirsalehi et al. (2025) published a recent article studying auditory deprivation and related changes in spatial memory and hippocampal structure in rats. This study initially measured rat hearing acuity via auditory brainstem response (ABR) to ensure normal pre-study hearing. These rats were then divided into multiple groups, including a control group and those receiving transcranial cochlear ablation at 14, 21, 28, or 60 postnatal days of age. After ablation and at four months of age, ABRs were repeated, which showed significant changes in the hearing acuity of the test groups. Of note, vestibular dysfunction was also excluded at this point. After ensuring hearing loss in the test groups and normal hearing in the control group, spatial memory was assessed via a water maze. This water maze evaluated a rat’s ability to navigate a complex environment and can help abstract spatial memory abilities. Hippocampal structure and function were also assessed via immunofluorescence sampling and Western Blot Analysis of a number of specific proteins, which are associated with synaptic plasticity and hippocampal neurogenesis.

Study findings suggested poorer spatial abilities, reduced neural plasticity, and poorer hippocampal function in rats with later ablation caused hearing loss. In other words, rats with earlier-induced hearing loss seemed to perform better on spatial ability tasks and had greater protein levels associated with neural plasticity and hippocampal function. Of note, human models have shown a correlation between hearing loss and reduced hippocampal volume. Auditory stimulation is thought to be paramount in the development of the hippocampus.

The researchers suggest that earlier hearing loss, during periods when neural plasticity is at its greatest, might allow rats to better develop brain structures associated with spatial learning. Furthermore, the hippocampus is still developing in younger mice (such as the 14-day cochlear ablation group), so having damage during these earlier stages may allow greater brain organization via neural plasticity following a significant change in hearing. Once brain structures are more fully formed and neural plasticity is less likely in older rats, hearing loss may have a greater and more permanent detrimental impact on the hippocampus and spatial learning.

Reference

Mirsalehi, M., Asghari, A., Rafsanjani, M.N.N. et al. (2005). Developmental timing of auditory deprivation influences spatial memory and hippocampal plasticity in rats. Scientific Reports, 15, 42695.