Home page
About the New Zealand HD Associations
Living with Huntington's Disease
Publications, press releases, conference information
HD Publications
Conference information
International news
Naturopathic Medicines and Therapies
Selected articles from HDA newsletters
News, articles and links to items of interest in HD research
New Zealand contacts
Acknowledgement and Disclaimer

4 Nov 2017

International Information

Information From Around the World
How Huntington’s 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 ventricles.

What Causes Huntington’s Disease?

Specifically affected are cells of the basal ganglia, structures deep within the brain that have a number of important functions, including coordinating movement.

Within the basal ganglia, HD especially targets neurons of the striatum, particularly those in the caudate nuclei and the pallidum. Also affected is the brain’s 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 Huntington’s 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.

Cortical Area Function
Prefrontal Cortex 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
Visual Cortex Detection of simple visual stimuli
Wernicke’s Area Language comprehension
Auditory Association Area Complex processing of auditory information
Auditory Cortex Detection of sound quality (loudness, tone)
Speech Center (Broca’s Area) Speech production and articulation

Some Definitions:

Brain

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 brain.

Forebrain

The largest division of the brain, which includes the cerebral cortex and basal ganglia. It is credited with the highest intellectual functions.

Amygdala

A structure in the forebrain that is an important component of the limbic system.

Basal Ganglia

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.

Brain Stem

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.

Cerebral Hemispheres

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, doesn’t write within lines). This problem is called Broca’s aphasia.

There is a region in the left temporal lobe called Wernicke’s area. Damage to this area causes Wernicke’s 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 Medical Definitions]

Cerebrum

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 cerebral cortex.

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.

Cerebral Cortex

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 callosum”.

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.

Cerebellum

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 one’s 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 person’s ability to walk, talk, eat, and to perform other self care tasks.

Corpus Callosum

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.

Hippocampus

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 movement.

Insula

The insula influences automatic functions of the brainstem. For example, when you hold your breath, impulses from your insula suppress the medulla’s breathing centers. The insula also processes taste information.

Limbic System

The limbic system is important in emotional behavior and controlling movements of visceral muscles (muscles of the digestive tract and body cavities).

Pituitary Gland

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 urine.

Thalamus

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 cerebral cortex.

Brain “Lobes”

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 spoken commands.

Frontal Lobe

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. Broca’s area, important in language production, is found in the frontal lobe, usually on the left side.

Parietal Lobe

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.

Occipital Lobe

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.

Temporal Lobe

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 Wernicke’s area (language and speech functions.)

Medulla

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.

Resources:

Neuronal Regions Affected - Huntington’s
http://srv2.lycoming.edu/~newman/courses/bio22298/disorderpapers/Huntingtons/preliminary.html

Neurosurgery On Call
http://www.neurosurgery.org/health/patient/answers.asp?DisorderID=51

What Causes Huntington’s Disease?
http://huntingtondisease.tripod.com/genetictesting/id85.html

Why Do Certain Symptoms Occur In Huntington’s Disease?
http://endoflifecare.tripod.com/huntdiseasefaqs/id92.html

How is HD Diagnosed?
http://huntingtondisease.tripod.com/genetictesting/id81.html

How Stuff Works [Brain]
http://health.howstuffworks.com/brain5.htm

http://www.sfn.org/content/Publications/BrainBackgrounders/glossary.htm

http://health.howstuffworks.com/brain.htm

Cerebral Hemispheres:
http://www.sfn.org/content/Publications/BrainBackgrounders/glossary.htm


Back to the top | Back to contents



Appreciation and thanks must go to Judy Lyon for compiling the wealth of information available
on this site, and to Graham Taylor for maintaining the original site for so long.

Home | About | Information | Resources | Newsletters | Research | Contacts | Disclaimer |
Original content © HD Associations of New Zealand