plasticity of the immature brain: sensory deprivation, focal lesions
DESCRIPTION
Plasticity of the Immature Brain: Sensory Deprivation, Focal Lesions. Shani Hagler Isabelle Rapin Child Neurology: September 25, 2013 No conflict of interest. Brain Plasticity. The structure of the brain is a function of the genetic programs that orchestrate its development and - PowerPoint PPT PresentationTRANSCRIPT
Plasticity of the Immature Brain:Sensory Deprivation,
Focal Lesions
Shani HaglerIsabelle Rapin
Child Neurology:September 25, 2013
No conflict of interest
Brain Plasticity
The structure of the brain is a function of
the genetic programs that orchestrate its
development
and
inputs from the environment
A. Sensory deprivation
Environmental effect on development of cortical neurons in fish:
Brought upalone
Brought up with others
Cover of
Science !
Brain Plasticity
In humans and animals
damage or sensory deprivation
→
structural alteration (limited) of subcortical relays and sensory cortex
potential for (partial) functional recovery / substitution
Brain Plasticity
Lack of major sensory input
(deafness, blindness, limb amputation, etc.)
→
major reorganization of sensory cortex, with spared modalities occupying (partially) deafferented sensory areas
Variables that affect brain reorganization
Age at sensory deprivation Completeness of the sensory loss Interval since sensory loss Stimulation following the sensory loss
Unilaterally Deafened Animals: Subcortical Plasticity
More immature animals → greater effect
Sound deprivation, cochlear destruction →
structural reorganization of brainstem
nuclei, competitive innervation
Decreased number, smaller neurons
Dendritic atrophye.g., Webster, Clopton, Parks, Rubel
Human: Subcortical Plasticity
Down infant (middle ear effusion) →
♦ ventral cochlear nuclei smaller; fewer neurons
Cockayne syndrome (cochlear degeneration) →
♦ ventral cochlear nucleus, medial olive, inferior
colliculus: neurons small
♦ medial geniculate, Heschl gyrus: neurons normal !
Gandolfi, 1981, 1993
Plasticity: Differences in Early Sound Exposure in Animals →
Decrease affects sound localization and visual/auditory maps in tectum
Patterned sound exposure affects sound selectivity of collicular neurons in rats, mice
Selective cochlear lesions change tonotopic map in auditory cortex in cats
Discrimination training changes tonotopic map in auditory cortex in owls
Deafness increase visual responses in auditory cortex in cats
Plasticity: Early Speech Sound Exposure in Humans
Neonate: makes many speech sound discriminations
1 year old: loss of irrelevant, honing of relevant speech sound discriminations
Toddler/preschooler: learn new language accent-free
Older child/adult: accented new language; do not hear irrelevant contrasts (e.g. L/R)
Bilateral Congenital Vestibular Dysfunction:
Effect on Sitting and Walking (N=22)
• No nystagmus or vertigo
• May have delayed head control, hypotonia
• Age at sitting: 8 months ( 6 – 24)
• Age at walking: 16.5 months (10 – 48)
• Danger: swimming under waterRapin 1974
Brain differences in early blindness
Normally - 1/3 of cortex involved in visual processing
Blinded animal studies: new projections from inferior colliculus (auditory) to lateral geniculate nucleus (normally visual)
Anatomy: - Gray&white matter atrophy of visual networks - Increase in cortical thickness in cuneus (decreased
pruning?)
Metabolism:- 15% ↑ glucose metabolism in striate and extrastriate cortex
Kupers et al, 2011
A. Gray matter - red, white matter - blueB. Increased cortical thickness of cuneusC. Increased glucose metabolism Kupers et al. 2011
Brain imaging in congenital/early blindness
Cross-modal plasticity Occipital cortex (OC) - shift from processing visual other sensory
modalities ? explains extraordinary auditory & tactile abilities in the blind
TACTLE: - ↑ tactile acuity - Braille activates OC only in congenital/early onset blindness - TMS disrupting occipital lobe errors in Braille & paresthesias in fingers - TDU (computer game) training for one week blind activated visual
cortex AUDITORY: - 1/2 EOB: ↑ localization mono-aural sound - activates specific OC areas
SPACIAL PERCEPTION: - CB unaffected by hand crossing in determining order of hand touched
Kupers et al 2011Ptito et al 2008
Cohen et al 1999Frasnelli et al 2011
Crossmodal plasticity in early blind
OLFACTION - ↑ odor identification - odor detection → ↑ blood oxygenation level-
dependent (BOLD) responses in primary & higher order olfactory & occipital cortices
HIGHER CORTICAL FUNCTION - repetition priming (-rTMS) over to visual
cortex → slows Braille reading
Kupers et al 2011
Brain consequence of sensory deprivation
Cortical reorganization hypothesis- cross-modal brain responses = formation of new pathways in the sensory-deprived brain
vs.Unmasking hypothesis
- loss of a sensory input → unmasking and strengthening of preexisting neuronal connections
Kupers et al 2011
Plasticity in focal early lesions in visual pathway
Less clearly correlated field cuts with early than late focal lesions
Infant with perinatal stroke of L optic radiations - at 3 months: visual cortical activation only of unaffected side - at 20 months: activation of visual cortex on affected side reorganization of thalamo-cortical pathway
Early visual field defecit - less ↓ in environmental navigation - in cats: entire visual cortex removed visual orientation
unaffected due to reorganization of subcortical to extrastriatal visual pathways
Seghier et al., 2004
-LEFT--potential by-pass of lesion potential full recovery of conscious vision.
-RIGHT-- no full recovery of conscious vision. Expanded collicular -- extrastriate cortex ~ normal visual exploration & navigation
Cionni et al 2011
Damage Lt optic radiation
Damage Rt striate cortex:
Early lesions in central visual pathway in cat
Hemiplegic CP
Corticospinal Tract Development Reaches cervical cord by 24 wks
Begins myelination by 40 weeks
Newborn: both ipsi- and contralateral corticospinal innervation of spinal motor neuron pools
By 2yrs - Rapid differential development of the ipsilateral and contralateral tracts. Dominance of the contralateral (crossed) tract
In hemiplegia: ipsilateral dominance progressively detrimental competes with residual contralateral tract
JA Eyre et al., 2007
Sensorimotor Reorganization in CP*
Motor: both ipsi- and contralesional cortical reorganization
Somatosensory: predominantly ipsilesional reorganization motor + sensory lesion: interhemispheric dissociation of motor/sensory functions
Motor cortex lesion – total loss of crossed tract rare- activity-dependent competition for ipsi- vs. contralesional access
to spinal motor neuron pool (TMS & EMG)- role of somatosensory feedback from affected limb
*pattern depends on timing, size, & location of lesion.
Guzzella et al. 2007
Main types of sensorimotor reorganization in lateralized damage
Cionni et al. 2011
CP & Hand Function
Finger dexterity: correlation atrophy of thalamo-cortical > than cortico-spinal tract
Contralateral slower than ipsilateral hand Bimanual: both slow “ : contralateral better than when
unimanual
Rose et al., 2011
Steenbergen et al., 2008
Hemiparetic CP in Perspective
• Dynamic motor deficit Immature cortico-spinal hemi not present beforeof 6 mos Worsening hemi: competition of uncrossed and crossed
cortico-spinal tracts tract for spinal motor neurons Very early lesion: uncrossed tract may compensate
• Importance of sensory deficit for prognosis
• If sensory & motor reorginization in different hemispheres severity of deficits poorly coordinated
• Neglect: Lt lesion ± mild bilateral
• Rt lesion ± ↓ attention, ↓ spacial skills
Katz et al 1998
B. Focal lesions
Language areas in the left hemisphere
Language in the brain:distributed network
Language processing is bi-hemispheric:♦ Lt >> Rt: phonology, syntax, semantics
♦ Rt >> Lt: prosody, pragmatics
♦ Both (L >> R): lexicon
Lt. superior temporal: phonologic decoding Lt. inferior frontal: encoding phonology/syntax Suprasylvian temporo-parietal: lexical processing Cerebellum: encoding automaticity etc. Etc.
Language in early lateralized brain lesion
Language will develop whether lesion in the Rt or Lt hemisphere (plasticity)
Location of lesion does not predict type of language deficit !!
Language is delayed, but catches up by school age
Price to pay for plasticity: visuo-spatial deficits likely
E. Bates et al.
Early acquired aphasia vs. developmental language disorder
Aphasia• Cause: early focal lesion• Language delayed• Lesion location:
• not predictive of type !• articulation: OK
Prognosis: • ~ good• reading ± OK• often ↓ visual/spatial skills
• CT/MRI: informative
Developmental• Cause: ~ genetic • Language delayed• Several subtypes:
• most receptive/expressive, • others expressive, fluent
Prognosis: • variable• reading ~ impaired• often: + other dev. disorder
• CT/MRI: ~ useless
Acquired aphasia in toddlers/older children
Parallel the aphasia syndromes of adults
Recovery of language tends to be better than in adults but is by no means necessarily complete
Sequelae: depend on size/location of lesion
Sequelae: almost invariably reading/ academic problems ± cognitive deficits
Cortical Calculation Networks
Dehaene, 2001
Calculation: Relevant Cortical Circuitry
Occipito-parietal (dorsal, “where”) visual stream intraparietal sulcus L > R
Occipito-temporal (ventral, “what”) visual stream fusiform gyrus
Lateral prefrontal cortex♦ Working memory
♦ Attention
♦ Executive skills
Dyscalculia
Difficulty acquiring basic arithmetic skills Detected later than dyslexia Requirements: adequate
♦ language skills♦ visuo-spatial skills♦ memory, working (& long-term)♦ executive skills, including attention
Children with dyscalculia Control children
Kucian et al. 2006
Gerstmann syndrome (1920s)
In acquired Lt ~ angular gyrus lesion♦ R-L confusion♦ Finger agnosia♦ Dyscalculia♦ Dysgraphia
Developmental Gerstmann syndrome (Kinsbourne & Warrington 1963)
♦ All of the above♦ Constructional dyspraxia
Stevenson et al., Science 1986
Roots of American lower SEM than Asians: School hours/week on
language vs. math
Japan Taiwan U.S.
INTERVENTION
Effect of Practice on the Brain
Violinists: ↑ cortical finger representation
Musicians vs non-musicians: altered hemispheric dominance for music
Wine tasters: much enhanced smell discrimintion
Dancers, athletes: enhanced cerebellar activation
Remediation
Training / education is the most powerful tool we have to alter / improve brain structure and function
But… brain plasticity is limited by♦ severity of pathology♦ location of pathology♦ age at time of insult♦ adequacy of the intervention!
Cochlear Implant
Requirement: viable neurons in spiral ganglion
Early in prelingual deafness: activates the central
auditory pathway → quite effective
Late in prelingual deafness: activates primary but
not secondary auditory cortex → more limited
effectiveness
In previously hearing person → effective
In all cases: requires intensive and prolonged
training