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CHAPTER 11
The Body Senses
and Movement
The Body Senses
Movement disorders
Learning disorders
Parkinson’s disease
• Parkinson’s disease: characterized by
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Motor tremors
Rigidity
Loss of balance and coordination,
Difficulty in moving, especially in initiating movements
• The symptoms are caused by deterioration of the substantia nigra.
– neurons of the substatia nigra send dopamine-releasing axons to the
striatum.
– The striatum: composed of the basal ganglia’s
• caudate nucleus and putamen
• nucleus accumbens.
– Upsets balance between direct and indirect pathways
etiology
• Some forms likely genetic:
– Recent whole-genome study of Parkinson’s patients identified 12 genes
that likely contribute to the disease.
– Two of the implicated genes may play role in the development and
programmed death of dopamine-producing neurons.
– Two others result in deviant proteins that are components of Lewy bodies
• Lewy bodies: abnormal clumps of protein that form within neurons.
– Lewy bodies found in several brain locations in some Parkinson’s patients
– Also found in people with form of dementia, dementia with Lewy bodies.
– Lewy bodies likely contribute to cognitive deficits and depression that
also often accompany Parkinson’s disease.
treatment
• Typically treated by administering levodopa (L-dopa),
– precursor for dopamine.
• Why use precursor?
– Dopamine not cross the blood-brain barrier
– L-dopa will
– in the brain is converted to dopamine.
• Problem:
– Treatments increase dopamine throughout brain
– Causes significant side effects including
• Restlessness
• involuntary movements
• hallucinations.
– As more neurons die, more drug is required, increasing the side effects.
– Eventually, no neurons left to treat!
Huntington’s cHorea
• Huntington’s disease
– Degenerative disorder of the motor system
– Cell loss in the striatum and cortex.
– Is genetic: dominant gene trait
• Progressive disorder
– Onset typically in late 20’s, early 30’s
– Years before a diagnosis, begins with jerky movements that result
from impaired error correction.
– At mid stage:
• involuntary movements appear
• first as fidgeting
• then as movements of the limbs
– Late stage:
• writhing of the body
• facial grimacing
• Loss of motor control and death
Huntington’s
•
Much more severe symptoms than Parkinson’s disease:
– Cognitive and emotional deficits are a universal characteristic of Huntington’s
disease
– In contrast to other movement disorders such as Parkinson’s.
– https://www.youtube.com/watch?v=JzAPh2v-SCQ
– https://www.youtube.com/watch?v=rplp3rGzn5Y
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Deficits include
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Impaired judgment
Difficulty with a variety of cognitive tasks
Depression, often with bipolar tendencies
Personality changes
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Motor symptoms are due to the degeneration of neurons in the striatum
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Defective or degenerated neurons in the cortex probably account for the
psychological symptoms.
etiology
• Huntington’s disease results for a mutated form of the
Huntingtin gene.
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Is dominant trait gene
If you have the gene, you will get the disease
50/50 chance of passing it on
Ethical dilemma created with identification of gene: Should
you be tested?
• The loss of neurons is probably due to the accumulation
of this gene’s protein excess
– Protein called huntingtin
– Function is unknown other than role in Huntington’s.
Myasthenia gravis
• Myasthenia gravis
– Disorder or muscular weakness
– Caused by reduced numbers of sensitivity of
acetylcholine receptors.
• Drugs that inhibit the action of AChe give
temporary relief from the symptoms of myasthenia
gravis.
– Remember: AChe breaks down Ach in synapse.
– Inhibitors increase amount of neurotransmitter available
at the neuromuscular junction.
Multiple sclerosis
• Motor disorder with many varied symptoms
– Caused by deterioration of myelin (demyelination) and neuron loss in the
central nervous system.
– Demyelination causes slowing or elimination of neural impulses
– This reduces the speed and strength of movements.
• As the disease progresses, unmyelinated neurons die, leaving areas
of sclerosis, or hardened scar tissue.
– Result: person experiences muscular weakness, tremor, impaired
coordination, urinary incontinence, and visual problems.
– Symptoms may wax and wane autoimmune reactions
• Several drugs are available: modify immune activity in multiple
sclerosis patients
– Slow the progress of the disease
– Do not repair the harm already done.
– Early detection and treatment is critical
Figure 11.23 The brain of a deceased MS patient
The arrows indicate areas of sclerosis, or hardened scar tissue.
Learning and
motor disruptions
• Strong link between descending motor pathway abnormalities and a
variety of genetic, behavioral, learning and psychological disorders.
• Learning and psychological disorders linked to descending motor
pathway disturbances include
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Dyslexia,
Tourette’s syndrome,
Several genetic forms of mental retardation
Autism
ADHD.
• The common link between all of these disorders: Inability to
appropriately inhibit some behavioral patterns while
disinhibiting others.
distonia
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Primary dystonia:
– Movement disorder resulting from basal ganglia dysfunction
– Some cognitive dysfunction, as well
– May be related to the ability to detect different emotional facial
expressions.
– https://www.youtube.com/watch?v=mJIBBGZfk44
• Patients with primary dystonia show isolated deficits in
– Recognition of disgust
– but NOT ability to detect happiness, surprise, sadness or anger
• Dystonia resulting from basal ganglia dysfunction demonstrates the
role of the basal ganglia in cognitive behavior such as emotion
recognition.
22q11.2 deletion syndrome
• 22q11.2 deletion syndrome (22qDS):
– Genetic “error”
– caused by the deletion of a small piece of chromosome 22.
• Children with 22qDS show a wide spectrum of disabilities
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cognitive and motor deficits
physical anomalies
ADHD,
poor executive visual attention,
poor sensorimotor processing,
learning disabilities with primary impairment in working memory.
https://www.youtube.com/watch?v=mrk_LUQXLOk
– up to 25 times more likely to develop autism, pervasive developmental
disorders, and schizophrenia.
•
may have early functional abnormalities in corticostriatal pathways
linking the prefrontal cortex and basal ganglia structures.
Lesch-nyan syndrome
•
Rare genetic disorder caused by a mutation in the gene coding for the enzyme
hypoxanthine-quanin phosphoribosyltransferase
• Characterized by
– hyperuricemia,
– motor disorders
– severe and compulsive self mutilation.
– https://www.youtube.com/watch?v=1U6LDpF_LFE
• linked to descending motor pathway dysfunction
•
Why? Disconnect between the prefrontal cortex and the basal ganglia
– caused by DA dysfunction
– Result: dysfunctional DA signal which accidentally reinforces early injurious
behavior
– Initial injurious behavior occurs because of motor dysfunction resulting in
clumsiness and awkward movements that incidentally produce self injury.
– Behavior becomes well learned and automated behavior
– Result: Pattern of severe self mutilation.
tourette’s syndrome
• Tourette syndrome (TS) characterized by
– Stereotyped involuntary movements, or tics.
– Result of structural and functional abnormalities of the basal
ganglia
– Link between motor system and limbic system is disturbed
– Result is spontaneous disinhibiton of competing motor and
limbic system
• Treatment:
– Typically: antipsychotic medication (Dopamine D2 antagonists)
because reduce available DA in system
– Unfortunately, compound learning deficits
– Alternative: biofeedback and learned control of tics
Language disorders
• Language disorders may be due to poor regulation by the basal
ganglia and related structures.
• Procedural deficit hypothesis (PDH) may explain specific language
impairments
– Disorder due to abnormal development of the basal ganglia
– Basal ganglia modulates the procedural memory system.
• Because of procedural memory functions, Basal Ganglia also
modulate:
– Learning and execution of specific motor and cognitive skills
– Especially skills critical for understanding and using aspects of grammar.
– Grammar involves word order, structure, rules for language
• Lexical (word) and declarative memory (memory for facts/basic
knowledge) not affected because these behaviors depend on
other brain structures
Speech apraxia
• Speech apraxia
– Difficulty with pronunciation, production of speech
– Particular phonemic characteristics of speech apraxia may be due to
subcortical dysfunction.
• Observations of those with speech apraxia show:
– Greater phoneme substitution errors than any other type of error
– Errors occur significantly more often in the initial rather than the
medial or final word position.
– These errors likely due to disinhibition of competing phonemes during
speech
– Suggests speech motor planning occurs at subcortical and cortical
brain levels.
stuttering
•
Strong link between stuttering and basal ganglia dysfunction.
– Stuttering similar to other basal ganglia disorders such as Parkinson’s
disease and dystonia.
– Stuttering is alleviated with interventions such as rhythm effects, chorus
speech, and singing: retraining brain
•
Basal ganglia-thalamocortical motor circuits through the putamen play a
key role in stuttering.
– Stuttering due to impaired ability of the basal ganglia to produce timing cues
for the initiation of the next motor segment in speech.
– Dysfunction due to abnormalities in the dopamine error-detection feedback
system,
– Pharmacologic interventions such as DA antagonists thus effective in
alleviating stuttering
• Also behavioral training programs: Singing
– Why? Singing involves rhythm, rate control, changes in intonation
– May allow alternative control of speech
adhd
• Descending motor system plays strong role in ADHD.
• Pattern of cognitive deficits consistent with prefrontal
executive problems: Individuals with ADHD may exhibit
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inattention,
difficulty with self regulation
response inhibition deficits (impulsivity)
restlessness or hyperactivity, and even apathy
• Exist at least two subtypes, according to the DSM-IV
– Inattention dimension: associated with significant neuropsychologic
impairment
– Hyperactive or impulsive dimension: no neuropsychologic impairments.
• Symptoms appear to be related to too much “disinhibition”,
ADHD and Brain changes
• Studies have shown: Children with ADHD have smaller
– Total cerebral volume.
– Frontal lobe volume
– Regions of the basal ganglia, particularly caudate nucleus
• Studies with typical children show that caudate size
decreases as child matures- result of normal “pruning” of
neurons.
• In contrast, children with ADHD:
– Appear to start out with smaller caudate nuclei,
– With maturation the decline is significantly greater than typicals
– The size differential of caudate nuclei between ADHD and typical
children increases with age.
• Right hemisphere structures more affected than left
hemisphere structures for children with ADHD
ADHD
• Several other related structures appear to be abnormal in children with
ADHD.
• Relative decrease in size of cerebellum
• Reduction in area of anterior or posterior corpus callosum
• ADHD may be due to a dysfunction of the prefrontal-subcortical
system:
– Children with ADHD may have delayed development in their frontostriatal
circuits.
– These circuits are understimulated, or under utilized
– Why do DA agonists (ritalin, adderall) work? Speed up system!