Biologic Development of the Auditory System Flashcards
Tectorial Membrane Development
Happens later in life–> low threshold signal detection and cochlear freq. selectivity are not evident until later stages of gestation (30-35 wks)
- -> 1st: Mid freq. develops and connects to brainstem
- -> base and apical regions develop later.
- 6 months after birth, high- and low freq thresholds continue to improve
When do we first “hear”
- connections of the cochlea to the brain are complete 10-20 weeks before birth
- ABR measured in premature neonates @15 wks
- Startle reflexes @24-25 weeks gestational age
Hearing Development
30-35 wks gestational: cochlear freq sensitivity present due to development of tectorial mebrane
Developmental Plasticity of the Binaural Hearing System: How we learned about it?
Studies of unilateral hearing loss (cochlear ablation or surgical removal)
Typical: medial and lateral nuclei of the SO and the medial nucleus of the trapezoid body receive input from both cochleas.
After removal of one cochlea, the nuclei received two inputs originating from the same side.
This changed the response properties of the neurons in the brainstem and the midbrain
Also, Sharma, Angelucci and Sur 2000 suggest sensory rerouting example: cells in the auditory cortex were driving by visual input
–> areas “devoted” to a sense can take the role for neural processing of a diff sensory modality. This space in the brain becomes available to process of the sensory modalities
Developmental Plasticity of the Binaural Hearing System: Relevance for Early Intervention Considerations
- impacts on the binaural auditory system
- possible lang delays can occur may not become apparent until later
- attempt to normalize hearing during early postnatal years
CIs: no matter duration of deafness, there is some benefit, but implanted before 5–> significantly better speech understanding and lang. development (Harrison, Gordon, and Mount, 2005)
