Neuropsychology of DeafnessJill M. PlevinskyJanuary 23, 2014

OutlineBrief etiology of deafness

Neuropsychological assessment of deaf persons

Developmental and cognitive implications of deafness

Neural and cortical plasticity associated with sensory loss

Neural and cortical plasticity associated with cochlear implants

Neurobiology of sign language

Social cognitive neuroscience insights from deafness

Anatomy and physiology of the ear and hearingThe pinna and external auditory canal form the outer ear, which is separated from the middle ear by the tympanic membrane. The middle ear houses three ossicles, the maleus, incus and stapes and is connected to the back of the nose by the Eustachian tube. Together they form the sound conducting mechanism. The inner ear consists of the cochlea which transduces vibration to a nervous impulse and the vestibular labyrinth which houses the organ of balance.

Etiology of deafnessType of hearing loss depends on where in the ear the

problem occurs

Three basic types: Conductive hearing loss

Occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the ossicles of the middle ear

Sensorineural hearing loss (SNHL) Occurs when there is damage to the inner ear (cochlea), or to

the nerve pathways from the inner ear to the brain Mixed hearing loss

Sometimes occurs in combination with SNHL, damage to the outer or middle ear and the inner ear or auditory nerve

Age of onset of deafnessPrelingually deaf

95% of all deaf children are prelingually deaf May be capable of oral communication, but usually develop

these skills much later than they developmentally should

Postlingually deaf Many retain their ability to use speech and communicate with

others orally

Causes of hearing loss in adultsOsteosclerosis

Meniere’s disease

Autoimmune inner ear disease

Very loud noise

Acoustic neuroma

Physical head injury

Presbycusis

Ototoxic medications Aminoglycoside antibiotics, salicylates (aspirin) in large quantities, loop diuretics,

drugs used in chemotherapy regimens

Hearing loss in older adults

• Hearing loss is one of the most common complaints in adults over the age of 60

• Individual differences in hearing ability predicted the degree of language-driven

neural activity during comprehension

• Linear relationship between hearing ability and gray matter volume in the primary

auditory cortex

• Declines in auditory ability lead to a decrease of neural activity during

processing of higher-level speech, and may contribute to loss of gray matter volume in

the primary auditory cortex

fMRI findings• A) Regions in which poorer-hearing

listeners showed less language-driven brain activity

• B) Overlap of these regions defined probably primary auditory cortex

• C) Strongest cortical connectivity is to the prefrontal cortex, followed by premotor and temporal cortices

Causes of hearing loss in childrenOtitis media: inflammation in the middle ear

Congenital hearing lossAutosomal dominant hearing lossAutosomal recessive hearing lossX-linked hearing lossPrenatal infections, illnesses, and toxins

Meningitis

Acquired hearing loss Infections, ototoxic drugs, meningitis, measles, encephalitis, chicken pox,

influenza, mumps, head injury, noise exposure

Assessing deaf and hard of hearing individualsCommunication mode and test administration

Use of interpreters

Selection of appropriate tests and test usage

Demographic factors influencing test interpretation

Impact of deafness on neuropsychological performance30-40% of those who are deaf or hard of hearing have

additional disabilities resulting from the same condition, disease, or accident that caused the hearing loss

Those with mild-moderate hearing loss are sometimes overlooked when it comes to other special needs because it’s assumed that their hearing devices compensate for their disability

Cognitive development in deaf childrenAcademic achievement

Reading development

Language development

Performance on standardized intelligence tests

Visual-spatial and memory skills

Conceptual development

Neuropsychological function

Cognitive development in deaf childrenAcademic achievement

Reading development

Language development

Performance on standardized intelligence tests

Visual-spatial and memory skills

Conceptual development

Neuropsychological function

Neural and cortical plasticity associated with sensory loss The process of developing a functional auditory system is affected significantly by

sensory deprivation

Sensory deprivation is associated with cross-modal neuroplastic changes in the brain

Deaf individuals show superior skills in perceptual tasks

Exact mechanisms of cross-modal plasticity and neural basis of behavioral compensation are largely unknown

Not all neuroplastic changes represent behavioral gains and the restoration of a deprived sense doesn’t automatically translate to it’s eventual function

Cochlear implantation• Surgically implanted devices providing a sense of sound

• Cochlear implants bypass damage to sensory hair cells in the cochlea by directly stimulating the auditory nerve and brain

• Candidates have to have severe-profound sensorineural hearing loss in both ears, a functioning auditory nerve, realistic expectations of results, support of family/friends

Neural and cortical plasticity associated with cochlear implantsThe optimal time to implant a young congenitally deaf child with a unilateral

cochlear implant is within the first 3.5 years of life when the central pathways show maximal plasticity

Neuronal mechanisms underlying sensitive periods for cochlear implantation Delays in synaptogenesis Deficits in higher order cortical development Cross-modal recruitment

Consequences of long-term auditory deprivation

a) Deaf children who receive a cochlear implant at 7 y.o. show abnormal cortical auditory evoked potentials and a lack of top-down modulation of incoming auditory stimuli

b) Long-term deafness beyond the critical period results in cross-modal cortical reorganization

c) Auditory deprivation can result in deficits in processing of multimodal stimulation necessary for language learning

Neurobiology of sign language• Distinctions between spoken language (SpL) and sign language

(SL)

• Neural systems supporting signed and spoken language are very similar – both involve a predominately left-lateralized perisylvian network

• The use of space in SL

• The role of the parietal cortex in SL processing

• The role of face and mouth in SL processing

Insights into social cognitionDevelopmental pathways for sociocognitive process are influenced by

“complex interaction effects of early temperament predispositions, socialization processes, relationship, and culture”

Visual attention Impulsivity and distractibility

High-level visual processing Facial expressions Human actions

Language and communication Theory of mind

ReferencesAlberti, P.W. (2001). The anatomy and physiology of the ear and hearing. Evaluation, prevention, and

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Calderon, R. (1998). Learning disability, neuropsychology, and deaf youth: Theory, research, and practice. Journal of Deaf Studies. 3, 1-3.

Corina, D. & Knapp, H. (2006). Sign language processing and the mirror neuron system. Cortex. 42, 529-539.

Corina, D. & Singleton, J. (2009). Developmental social cognitive neuroscience: Insights from deafness. Child Development. 80, 952-967.

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References (cont.)Kral, A. & Eggermont, J.J. (2007). What’s to lose and what’s to learn: Development under auditory deprivation, cochlear implants and limits of cortical plasticity. Brain Research Reviews. 56, 259-269.

Kral, A. & Sharma, A. (2011). Developmental neuroplasticity after cochlear implantation. Trends in Neuroscience. 35, 111-122.

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Mayberry, R.I. (2002). Cognitive development in deaf children: The interface of language and perception in neuropsychology. In S.J. Segalowitz & I. Rapin (Eds.), Handbook of Neuropsychology (2nd ed.). (pp. 71-107). New York, NY: Elsevier Science, Inc.

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Sharma, A., Nash, A.A., & Dorman, M. (2009). Cortical development, plasticity and re-organization in children with cochlear implants. Journal of Communication Disorders. 42, 272-279.