How Huntingtons Disease Affects The Brain
A Compilation of Facts
By Jean Miller
First, and foremost, as most of you know I am in NO way, shape or form a
medical or clinical professional nor do I have any plans to become one! I am only
one human being who has lived with Huntington's Disease since 1983 and, over those years,
have learned that HD affects people differently primarily because of how the disease
affects different area's of the brain. So, in my unprofessional opinion,
atrophy of specific area's in the brain caused by Huntington's disease can be directly
related to the changes seen in an individual's judgment, memory, and other cognitive
functions experienced in people with HD.
To this end, I have always turned to literature explaining our
brain, "a little organ about the size of a small head of cauliflower".
Some of this material would take a rocket-scientist to understand, others
are simple enough for anyone to understand however lack information on how changes to a
specific area of the brain affect certain physical or cognitive symptoms in people.
The attached is a compilation of facts on the brain that I've found that I'm
hoping might help people better understand how degeneration in a given part of the
brain affects their control over specific functions of their mind and body. It's not
the most simplest of explanations, so under the specific areas of the brain I've
highlighted [in red] the functions they control to better understand why we
might see the symptoms we see in Huntington's disease.
However, remember not all things scientific are absolute [from a lay-person's
perspective]! According to a scan my daughter Kelly had about 4 years before
she died, the neurologist wrote in her medical file [not telling me a scan had even been
taken] "This patient's caudate nuclei is totally absent. It's
remarkable she's not in a persistent vegative state." Kelly was still very
much aware and able to communicate, although with some difficulty!
I hope you find it interesting! If nothing else, maybe it would be good for
students wanting to learn more about HD and how it affects those with the disease!
Brain Section Affected By HD
Basal ganglia; cerebral cortex; caudate
nuclei and putamen; pallidum subcortical nuclei; the frontal and temporal lobes; and
What Causes Huntingtons Disease?
Specifically affected are cells of the basal ganglia,
structures deep within the brain that have a number of important functions, including
Within the basal ganglia, HD especially targets neurons of the striatum, particularly those in
the caudate nuclei and the pallidum. Also affected is the brains
outer surface, or cortex, which controls thought, perception, and memory.
Those with HD may show shrinkage of some parts
of the brain - particularly two areas known as the caudate nuclei and putamen - and enlargement of cavities within
the brain called ventricles. [from: How is HD Diagnosed]
Why Do Certain Symptoms Occur In
Huntingtons Disease (HD)- A Tour Through the Brain.
The brain sits in the
skull and has a jelly-like consistency. Over its surface, there are many folds and
crevices. Multiple folds are grouped together under the term, lobe. The lobes
of the brain have names and take on certain functions. These functions are not completely
understood and often have more than one location, but some general statements can be made:
The Lobes [see their functions below]
In HD, there is a tendency for the frontal and temporal lobes to be affected.
Nothing is absolute and each case is different. However, after realizing that the frontal
and temporal lobes experience major problems with executing their function in HD, some
common symptoms in HD become more understandable.
Some of the common symptoms in HD are coordination problems,
concentration difficulties, less judgement, planning difficulties, decrease memory
ability, emotional withdrawal, and less emotional control. These symptoms are at least
partially tied to dysfunction of the frontal and temporal lobes.
Sensory function, perception of touch and recognition of space relations are usually not
affected or minimally involved in HD.
Deeper in the brain, below the lobes, are places referred to subcortical nuclei. These
centers have to do with motor execution and control, among other functions. These are
also affected in HD and their dysfunction can create involuntary movements, abnormal
swallowing, balance problems, and speech difficulty.
Problem Solving, Emotion, Complex Thought
Motor Association Cortex
Coordination of complex movement
Primary Motor Cortex
Initiation of voluntary movement
Primary Somatosensory Cortex
Receives tactile information from the body
Sensory Association Area
Processing of multisensory information
Visual Association Area
Complex processing of visual information
Detection of simple visual stimuli
Auditory Association Area
Complex processing of auditory information
Detection of sound quality (loudness, tone)
Speech Center (Broca’s Area)
Speech production and articulation
The brain is made up of many different areas,
each having a particular structure and function. To separate the brain into right and left
hemispheres, you need to cut the brain in the midsagittal plane. But the human
brain is unique. It gives us the power to think, plan, speak, imagine. It is truly an amazing organ. The surface area of
the brain is about 233 to 465 square inches (1,500 to 2,000 cm2). To fit this
surface area within the skull, the cortex is folded, forming folds (gyri)
and grooves (sulci).
The brain performs an incredible number of tasks:
It controls body temperature, blood pressure, heart
rate and breathing.
It accepts a flood of information about the world around you from your various senses (eyes,
ears, nose, etc.).
It handles physical motion when walking, talking, standing or sitting.
It lets you think, dream, reason and experience emotions.
All of these tasks are coordinated, controlled
and regulated by an organ that is about the size of a small head of cauliflower: your
The largest division of the brain, which includes the cerebral cortex
and basal ganglia. It is credited with the highest intellectual functions.
A structure in the forebrain that is an important component of the limbic system.
Clusters of neurons, which include the caudate
nucleus, putamen, globus pallidus and substantia nigra, that are located deep in the brain
and play an important role in movement.
Originating in the brain stem are ten of the
twelve cranial nerves that control hearing, eye movement, facial
sensations, taste, swallowing and movement of the face, neck, shoulder and tongue muscles.
The cranial nerves
for smell and vision originate in the cerebrum. Damage in this area may readily affect
these nerves causing, for example, one eye to turn in and the complaint of
double vision or drooping of one side of the mouth with drooling.
The two specialized halves of the brain. In
general, the left hemisphere or side of the brain is responsible for language and speech. Because of
this, it has been called the dominant hemisphere. The right hemisphere
plays a large part in interpreting visual information and spatial processing. In about one
third of individuals who are left-handed, speech function may be located on the right side
of the brain. Left-handed individuals may need specialized testing to determine if their
speech center is on the left or right side prior to any surgery in that area.
There is an area in the frontal lobe of the left
hemisphere called Broca\xd5s area. It is beside the region that controls the movement
of our facial muscles, tongue, jaw and throat. If this area is destroyed, there is difficulty in
producing the sounds of speech. One is unable to move the tongue or facial
muscles in the appropriate way to make words. The individual can still read and understand
spoken language but has difficulty in speaking and writing (i.e. forming letters and
words, doesnt write within lines). This problem is called Brocas aphasia.
There is a region in the left temporal lobe called Wernickes area. Damage to this
area causes Wernickes aphasia. Words are heard but are meaningless (receptive
aphasia). An individual can make speech sounds. These
sounds however have no meaning for the individual is unable to understand what is said by
him or others.
Many neuroscientists believe that the left
hemisphere and perhaps other portions of the brain are important in language. An aphasia
is simply a disturbance of language. Certain parts of the brain are responsible for
specific functions in language production. There are many types of aphasias, each
depending upon the brain area that is affected, and the role that area plays in language
production. [See HD
The Cerebrum, the
main upper mass of the human brain, fills the top of the skull. It is considered the base
of conscious mental processes. Resembling a giant wrinkled walnut, it makes up
seven-tenths of the entire nervous system. The surface layer of the cerebrum is termed the
The cerebrum consists of the cortex,
large fiber tracts (corpus callosum) and some deeper structures (basal
ganglia, amygdala, hippocampus).
The outermost layer of the cerebral hemispheres
of the brain. It is responsible for all forms of conscious experience,
including perception, emotion, thought and planning. It integrates information from all of the sense organs, initiates motor
functions, controls emotions and holds memory and thought processes (emotional expression
and thinking are more prevalent in higher mammals).
The cerebrum is divided into two almost
identical hemispheres. It is split lengthwise down the middle and connected deep
down, near the center of the brain. Each hemisphere is divided into four lobes.
The word cortex comes from the Latin
word for bark (of a tree). This is because the cortex is a sheet of tissue
that makes up the outer layer of the brain. The thickness of the cerebral cortex varies
from 2 to 6 mm. The right and left sides of the cerebral cortex are connected by a thick
band of nerve fibers called the corpus
The cerebral cortex contains the gray matter of
the brain and the prefrontal area of the cerebral cortex comprises a larger portion of the
human brain. Located in the outermost layer of the cerebral hemispheres of the brain it is
responsible for all forms of conscious experience,
including perception, emotion, thought and planning. Language centers are
usually found only in the left cerebral hemisphere.
The brain stem is located in front of the
cerebellum and may be considered as a stem or structure holding up the
cerebrum. It consists of three structures: the midbrain, pons and medulla oblongata. It
serves as a relay station, passing messages back and forth between various parts of the
body and cerebral cortex.
Many simple or primitive functions that are
essential for survival are located here.
The word cerebellum comes from the
Latin word for little brain. The cerebellum is located behind the brain stem.
In some ways, the cerebellum is a bit like the cerebral cortex.
The cerebrum, which forms the bulk of the brain,
may be divided into two major parts: the right and left cerebral hemispheres. The cerebrum
is often a term used to describe the entire brain. It is divided into hemispheres and has
a cortex that surrounds these hemispheres. It is separated from the cerebrum by the
tentorium (fold of dura).
The cerebellum is the portion of the brain
(located at the back) beneath the occipital lobes, which helps coordinate movement (balance and muscle coordination). It fine
tunes our motor activity and helps us maintain our posture, our sense of balance or
equilibrium by controlling the tone of our muscles and senses the position of our limbs.
The cerebellum is important in ones
ability to perform rapid and repetitive actions such as playing a video game. Damage
affecting the cerebellum may cause an individual to stagger and
sway when he/she walks or has jerky movements of the arms and legs (a drunken appearance). An individual trying to reach an object may misjudge the distance and
location of the object and fail to reach the object. In the cerebellum, right-sided
abnormalities produce symptoms on the same side of the body. Damage may result in ataxia
which is a problem of muscle co-ordination. This can interfere with a persons
ability to walk, talk, eat, and to perform other self care
A large bundle of nerve fibers linking the left
and right cerebral hemispheres. The corpus callosum connects the two halves of the brain
and delivers messages from one half of the brain to the other.
A seahorse-shaped structure located within the
brain and considered an important part of the limbic system. It functions in learning,
memory and emotion. It is a small structure that contains nerve connections that send messages
to the pituitary gland.
The hypothalamus handles information that comes
from the autonomic nervous system. It plays a role in controlling our behavior such as eating, sexual
behavior and sleeping, and regulates body temperature, emotions, secretion of hormones and
The insula influences automatic functions of the
brainstem. For example, when you hold your breath, impulses from your insula suppress the
medullas breathing centers. The insula also processes
The limbic system is important in emotional behavior and
controlling movements of visceral muscles (muscles of the
digestive tract and body cavities).
The pituitary gland develops from an extension
of the hypothalamus downwards and from a second component extending upward from the roof
of the mouth. These two components form the pituitary gland which sits in a specialized
boney container at the base of the skull called the pituitary fossa.
It is involved in controlling a number of hormonal functions including thyroid functions, functions of the adrenal glands, growth and
sexual maturation. The posterior part of the pituitary gland regulates the formation of
The thalamus serves as a relay station for
almost all information that comes and goes to the cortex. The thalamus relays information
from most sensory organs to the outer region of the cerebrum or cerebral cortex; receives
and processes messages from the body concerning heat, cold, pain, pressure, touch; attention and
alertness, and influences motor activity of the
Each hemisphere of the brain has a frontal,
temporal, parietal and occipital lobe. Each lobe may be divided, once again, into areas
that serve very specific functions. It must be remembered that each lobe of the brain does
not function alone. There are very complex relationships between the lobes of the brain.
Messages within the brain are delivered in many
ways. The signals are transported along routes called pathways. Any destruction of brain tissue can disrupt the
communication between different parts of the brain. The result will be a loss of function
such as speech, ability to read or ability to follow simple
Front part of the brain, the anterior (front)
portion of the frontal lobe, is called the prefrontal cortex.
The prefrontal cortex plays an
important part in our memory, intelligence, concentration, temper and
personality. The premotor cortex is a region
found beside the primary motor cortex or precentral gyrus. These regions are found in the
frontal lobes.It guides our eye and head movements and sense of orientation. Brocas
area, important in language production, is found in the frontal lobe, usually on the
Sensory function, perception, recognition of space
relations. The parietal lobes interpret, simultaneously, sensory signals received from
other areas of the brain such as our vision, hearing, motor, sensory and memory. Together,
memory and the new information that is received give meaning to objects.
This region is called the visual cortex.
The occipital lobe on the right interprets visual signals from your left visual space,
while the left occipital lobe does the same for your right visual space. Damage to one
occipital lobe may result in loss of vision in the opposite visual field.
Memory, emotional control, language. The primary auditory cortex helps us hear sounds and gives sounds
their meaning, e.g. the bark of a dog. The temporal lobes are the primary region
responsible for memory. It contains Wernickes area (language and speech functions.)
The lower area of the brain known as the medulla
controls our heart rate, breathing, blood pressure, heart
rhythms, swallowing, vomiting, salivation, coughing and other automatic functions. These functions are important to our survival. Messages from the cortex to
the spinal cord and nerves that branch from the spinal cord are sent through the pons and
the brain stem. Because of the importance of these functions, damage to this area of the
brain and spinal chord is very dangerous. Destruction of these regions of the brain will
cause brain death.
Neuronal Regions Affected - Huntingtons
Neurosurgery On Call
What Causes Huntingtons Disease?
Why Do Certain Symptoms Occur In Huntingtons Disease?
How is HD Diagnosed?
How Stuff Works [Brain]