BRAIN Function and Disorder

 

• Amygdala

The amygdala is a almond-shaped structure adjacent to the hippocampus. located deep inside the temporary loab It is a crucial part of the limbic system, a group of structures involved with emotional responses and behavior. The amygdala is responsible for several functions, such as processing fear–learning and other related emotions and  It links areas of the cortex that process “higher” cognitive information with hypothalamic and brainstem systems that control “lower” metabolic responses (e.g. touch, pain sensitivity, and respiration).

This allows the amygdala to coordinate physiological responses based on cognitive information – the most well–known example being the fight–flight–or–freez response.

The amygdala has three functionally distinct parts

1. the medial group of subnuclei has many connections with the olfactory bulb and olfactory cortex,
2. the basolateral group has extensive connections with the cerebral cortex, particularly the orbital and medial prefrontal cortex,
3. the central and anterior group of nuclei has many connections with the brainstem hypothalamus, and sensory structures.

When the amygdala sustains damage, it can impair these functions and interfere with emotional and behavioral processes. As a result, individuals may experience problems with memory, decision-making, and other behavioral skills (mood swings, irritability, and even aggression).Some of the most common symptoms of amygdala damage include:

• Amygdala hijack: is a term used when the amygdala becomes overwhelmed by stress, “hijacking” the logical and rational centers of the brain. Sensory input passes by the amygdala before being transmitted to the more rational areas of the brain, such as the prefrontal cortex. When this occurs, the brain releases two stress hormones, cortisol and adrenaline, which help prepare the body for “fight or flight.” As a result, individuals may experience a rapid heartbeat, sweaty palms, goosebumps on the skin, dilated pupils, increased blood flow to the muscles, and increased glucose (blood sugar) levels.

• Memory Loss: occurs when the amygdala, which is responsible for encoding the emotional aspect of memory,

• Impaired Decision-Making: can be caused by damage to the amygdala or orbitofrontal cortex. 

• Anxiety and/or Depression: are two common secondary effects of a TBI that can occur after damage to the amygdala,

damage to the amygdala Turn of the fear response

Case study

The neurological patient SM has extensive damage to the amygdala in each hemisphere. She has no motor, sensory, or cognitive deficits. When asked to identify photographs of a series of facial expressions, SM could identify every expression but one, she could not recognize fear. Similarly, when asked to draw facial expressions, SM produced accomplished pictures of each emotion, but she could not reproduce the expression of fear. When asked about her drawings, she explained that 'she did not know what an afraid face would look like.'

Associated functions

fear–processing

emotion processing

learning

fight–or–flight response

reward–processing

Associated cognitive disorders

Many studies have linked autism with amygdala dysfunction. The lack of empathy often shown by autistic individuals has associated with the amygdala (Blair, 2008). Neural activity in the amygdala has also been strongly linked to depression (Northoff, 2007) and bipolar disorder (Phillips&Vieta, 2007). There is very strong evidence linking post–traumatic stress disorder with amygdala responses (Brewin, 2008).

Associated with damage

Aggression

Irritability

Loss of control of emotion

Disruption of short–term memory

Deficits in recognizing emotions (particularly fear)

Research reviews

• Blair (2008) discusses two disorders, psychopathy and autism, in relation to abnormal amygdala functioning (PMID: 18038346).
• Brewin (2008) reviews neurological correlates of post–traumatic stress disorder, which has been strongly linked to the amygdala (PMID: 18037017).
• Phillips and Vieta (2007) consider functional abnormalities of the amygdala as potential biomarkers of bipolar disorder (PMID: 17562698).
• Morrison and Salzman (2010) review the different roles of the amygdala, including coordinating affective/emotional responses (PMID: 20299204).
• Northoff (2007) reviews the neuropathology of depression, which has been linked with abnormal neural activity in a number of structures, including the amygdala (PMID: 17379318).
• Roozendaal and colleagues (2009) review studies that found neural correlates of stress–induced modulation of the amygdala (PMID: 19469026).
• Crocker and colleagues (2013) review evidence for cognitive biases and deficits in depression and anxiety, and how they interact with emotional processes (PMID: 23781184).

• Basal Ganglia

The basal ganglia comprise a group of structures that regulate the initiation of movements, balance, eye movements, and posture. They are strongly connected to other motor areas in the brain and link the thalamus with the motor cortex.

The basal ganglia are also involved in cognitive and emotional behaviors and play an important role in reward and reinforcement, addictive behaviors and habit formation.located deep within the brain. Each structure in the basal ganglia has its own specific function, but they all play a role in motor control, particularly the initiation and execution of skilled movements.

Normally, the brain is in constant communication with your muscles via neural pathways. However, when the basal ganglia sustain damage, some of these pathways can be affected and impair the brain’s ability to control your muscles.

When someone sustains basal ganglia brain damage, they may experience difficulties with balance, posture, or other movements. Fortunately, the brain has the ability to rewire itself through neuroplasticity, and there are many ways to treat basal ganglia brain damage and promote recovery.some of the most common secondary effects of basal ganglia brain damage:

• Chorea: is a condition caused by damage to the basal ganglia in which small, random, repetitive movements transition abruptly from one part of the body to another. A secondary type of chorea involves an aggressive, involuntary flinging of one arm, also known as hemiballismus.

• Athetosis: Similar to chorea is a condition known as athetosis– a stream of slow, flowing, writhing movements. This usually occurs in the hands and feet.

• Dystonia: when the basal ganglia cannot suppress the antagonist muscles after a brain injury, (dystoniamay) occur. Dystonia refers to uncontrollable, abnormal movements, resulting in symptoms such as foot cramping, rapid blinking, and trembling. Involuntary muscle contractions can occur in only one part of the body, known as focal dystonia. Segmental dystonia means two or more adjacent muscle groups are affected simultaneously, 

• obsessive-compulsive disorder: The basal ganglia are connected to the prefrontal cortex, which is an area of the brain that helps regulate behavior. (Studies) indicate the basal ganglia facilitate wanted behaviors and stop unwanted behaviors. Therefore, when the prefrontal cortex and basal ganglia are impacted by injury, excessive thoughts and repetitive behaviors, like obsessive-compulsive disorder, can result. Obsessive-compulsive disorder is often associated with “perfectionism” or keen attention, but these qualities are all encompassing of OCD. Survivors with this disorder may also experience intrusive thoughts, obsessions, and/or compulsions.

• Parkinsonism: can often include resting tremors, stiff muscles, impaired speech, delayed movements, or difficulty walking and balancing. Those who develop parkinsonism may also experience uncontrolled, repetitive movements like “tics” or make involuntary noises. Consult with your doctor or neurologist to obtain a proper diagnosis and treatment.

Pathways are best enhanced through repetitive exercise, or massed practice. Therefore, one of the most important ways to improve the effects of basal ganglia damage is by exercising your affected muscles.

Case Study

A 2008 study by Das and colleagues that approximately 5% of apparently healthy middle–aged adults have micro–lesions in the basal ganglia. Known clinically as silent cerebral infarcts (SCI), these lesions have an overall prevalence of about 10% in seemingly healthy adults.

Associated functions

Movement regulation

Dkill learning

Habit formation

Reward systems

Associated cognitive disorders

The basal ganglia are particularly associated with movement disorders such as Parkinson's and Huntington's disease. In terms of cognitive disorders, basal ganglia abnormalities have been found in individuals with schizophrenia, and may explain habit learning deficits associated with the disorder (Keri, 2008). The basal ganglia may also contribute the neuropathology of depression, particularly in relation to the limbic system (Stathis and colleagues, 2007).

Associated with damage

Tremors

Involuntary muscle movements

Abnormal increase in muscle tone

Difficulty initiating movement

Abnormal posture

Substructures

Caudate nucleus

Globus pallidus

Nucleus accumbens

Putamen

Substantia nigra

Subthalamic nucleus

Research reviews

• Das and colleagues (2008) examine neuroimaging data from over 2040 middle–aged participants and find evidence of silent cerebral infarcts in 10.7% of the sample (PMID: 18583555).
• Keri (2008) includes the basal ganglia in a review on category–learning deficits in schizophrenia (PMID: 17854895).
• Foerder and Shohamy (2011) review the role of the basal ganglia in non–declarative memory, motivation, and decision making (PMID: 21945835).
• Stathis and colleagues (2007) review associations between the basal ganglia, limbic system, and cognitive disorders with an emphasis on neuromodulation (PMID: 17691350).
• Yoon and colleagues (2013) suggest a relationship between the prefrontal basal ganglia and schizophrenia (PMID: 23290498).

• Brain Stem

The brain stem consists of a group of structures that lie deep within the brain, located at the base of the skull directly above the spinal cord. It connects the brain and spinal cord, which transports messages via neural pathways throughout the body. The brain stem is also responsible for critical functions that keep you alive and aware of your surroundings, making it one of the most important areas of the brain.

The brain stem is comprised of three distinct sections, which each section contributing to different functions:

• Midbrain. At the top of the brain stem rests the midbrain. This structure plays a large role in muscle movement, particularly eye movement.
• Pons. Below the midbrain lies the pons. The pons acts as a bridge between the cerebellum and spinal cord and helps control your balance, among other things.
• Medulla. Finally, at the bottom of the brain stem is the medulla. The medulla oversees essential life functions, such as breathing, heart rate, and swallowing.

So it plays an important role in maintaining homeostasis by controlling autonomic functions such as breathing, heart rate, and blood pressure. While the brain stem can organize motor movements such as reflexes, it coordinates with the motor cortex and associated areas to contribute to fine movements of limbs and the face.

damage to the brain stem can also affect other functions besides the ones listed above. Brain stem damage is rare. Most injuries to the brain stem are the result of swelling in other areas of the brain as swelling forces the brain stem against the skull. Regardless of how brain stem damage occurs, there are various effects associated with this type of brain injury. Many of them affect basic life functions. Because every brain injury is different, brain stem injury survivors may experiences some, all, or none of the possible effects.

Here are some of the most common effects of brain stem damage:

• COMA

The brain stem houses a network of neurons called the reticular activating system, which is responsible for states of consciousness and your ability to wake up. When the brain stem sustains damage, the reticular activating system can be affected and result in a coma.

Most comas after brain injury will last until the swelling goes down. After that, a person will usually pass through three (stages of consciousness) before finally becoming alert.

These stages are:

• Vegetative state. Eyes may open and shut but the person cannot respond in a meaningful way, like squeezing your hand.
• Minimally conscious state. Person can respond by blinking or smiling but falls in and out of consciousness.
• Confusional state. Person is awake and aware but does not have full control over their behavior.

The faster the person progresses through these stages, the (higher their chances) of making a full recovery will be.

• Locked-in Syndrome

One of the most severe effects that can occur after damage to the brain stem is locked-in syndrome. This condition causes full paralysis of the body except for the eyes.

This is a motor issue, meaning it only affects a person’s ability to move. Everything else about the individual — including their ability to think, reason, and hear everything going on around them — remains functional.

Because locked-in syndrome is a serious condition, most people do not regain movement, although (some have).

Supportive care is often the best option for survivors with locked-in syndrome. There are also computer programs that track eye movement so that the individual can communicate using specific eye movements.

• Swallowing problems

The medulla (the bottom section of the brain stem) controls various basic life functions including swallowing. When this section of the brain stem sustains damage, it can cause swallowing problems such as dysphagia.

• Respiratory problems 

The medulla also helps control breathing by sensing the level of carbon dioxide (CO2) in the blood and adjusting your respiratory rate in response.

However, a damaged medulla cannot detect how much CO2  is in the blood. As a result, it doesn’t know how much air the body still needs. This can cause breathing problems for brain stem injury survivors.

The most common respiratory problems after brain stem damage include:

• Hyperventilation: breathing too much too fast
• Hypoventilation: breathing too little too slow
• Apneustic breathing: problems exhaling air
• Apnea: lack of breathing

When breathing issues are severe, the survivor requires a ventilator until respiratory function returns to normal. There are also some medicationsthat help regulate breathing patterns and stimulate brain stem activity.

• Motor Difficulties

Although motor difficulties are not explicitly associated with brain stem damage, it’s worth mentioning as brain stem damage is often caused by an injury elsewhere in the brain.

For example, directly connected to the pons is the cerebellum, which controls balance and coordination. When the cerebellum sustains damage, it can impair an individual’s balance, resulting in a condition called ataxia.

While ataxia is associated with cerebellar damage, it can often coincide with brain stem damage due to close proximity.

Furthermore, movement is a brain-wide process. While the cerebellum controls balance, there are many other areas of the brain that contribute to movement, such as the motor cortex. Therefore, if more than the brain stem was impacted by injury, motor issues can occur.

Case Study

Cattaneo and colleagues (2006) describe two patients with damage (stroke) to the brain stem who had considerable difficulty balancing and walking. In addition, both were afflicted with “pathological yawning”, which occurred at a frequency of every 2 to 3 minutes.

Associated functions

maintaining homeostasis by controlling autonomic functions (including blood pressure, breathing, digestion, heart rate, perspiration and temperature)

alertness

sleep

balance

startle response

Associated cognitive disorders

Very few cognitive disorders have been associated with the brain stem. A number of studies have found brain stem abnormalities in individuals with autism (e.g. Rodier, 2003).

Associated with damage

• organ failure sleep disorders (e.g. insomnia, sleep apnea)
• difficulties balancing and moving

Substructures

medulla oblongata

midbrain

pons

Research reviews

Cattaneo and colleagues (2006) report two cases of pathological yawning following stroke damage to the brain stem (PMID: 16174652).

Rodier (2003) reviews evidence for brain stem injury in autism (PMID: 12349873).

Jou and colleagues (2008) find a significant difference in the gray matter of the brainstem of autistic boys compared with non–autistic boys (PMID: 18812009).

• Broca’s Area 

Broca's area is a functionally defined structure in the left frontal lobe of about 97% of humans (including a large majority of left–handers). Broca's area is involved mainly in the production of spoken and written language and also in language processing and comprehension. It takes its name from the French scientist Pierre Paul Broca whose work with language–impaired patients led him to conclude that we speak with our left–brain.

Damage to Broca’s area, a small region located in the frontal lobe, can lead to a speech disorder known as Broca’s aphasia or expressive aphasia. Individuals with Broca’s aphasia have difficulty forming words and producing speech and is responsible primarily for planning the motions .

Additionally, Pierre’s research has helped us obtain a better understanding of speech production, language processing, and comprehension of complex sentences, all of which can be affected by damage to Broca’s area Individuals with this speech disorder can typically understand what others are saying, but have difficulty finding their words and forming sentences verbally.

Brain injuries involving the frontal lobe of the brain may result in damage to Broca’s area. While the frontal lobe is one of the most common areas of the brain affected by a TBI, every brain injury is different, and survivors may experience a variety of secondary effects depending on the location and severity of the injury. 

There are many conditions that may result in damage to Broca’s area, including stroke, traumatic brain injury, tumors, and brain infections. The most common symptom of damage to Broca’s area is expressive (or non-fluent) aphasia. While there are many types of aphasia, expressive aphasia in particular is caused by damage to Broca’s area. Hence, it is also known as Broca’s aphasia.

Often along with frustration, symptoms of Broca’s aphasia may include:

• Difficulty finding the appropriate word to speak
• Speaking in phrases limited to less than four words
• Irregular rhythm of speech
• Pausing excessively when attempting to speak
• Difficulty repeating what others said
• Trouble following directions
• Poor or absent grammar used
• Difficulty understanding complex sentences
• Mild reading impairment, especially when reading aloud
• Difficulty with writing
• In severe cases, mutism (inability to speak)

Additionally, some individuals may omit using certain pronouns and conjunctions such as “the,” “an,” or “is” in their sentences. For example, an individual with Broca’s aphasia may say “me, cup” rather than “I want the cup” when asking for something. Due to the location of Broca’s area, some individuals with Broca’s aphasia may also demonstrate weakness or paralysis on one side of their body (typically the right).

Injury to the brain can destroy connections within the brain called neural pathways. When this occurs, the brain cannot communicate properly with certain parts of the body, interfering with functions such as speech and language. Fortunately, the brain has the ability to heal and rewire itself through a phenomenon called neuroplasticity.

To stimulate the brain and activate neuroplasticity, it’s crucial to practice high repetition of exercises, or massed practice. 

Repeating a skill helps stimulate the brain and reinforce the neural pathways for that skill. Therefore, consistent practice is important to improve damage to Broca’s area and overcome expressive aphasia.

Case Study

In the 1960s, Roger Sperry and Michael Gazzaniga devised an ingenious experiment to determine whether language was lateralized to the left hemisphere. They worked with split–brain patients (patients who had the connective tissue between right and left hemispheres removed). Using the left hemisphere, split–brain patients could produce the name of objects held in the right hand without difficulty. Amazingly, if they held the same object in the left hand (which is controlled by the right hemisphere), the object could not be named.

Associated functions

• language production (both speech and sign)
• comprehension of complex syntax

Associated cognitive disorders

Language impairments in autism may be related to abnormalities in Broca's area (see Bauman and Kemper, 2005).

Associated with damage

• Broca's aphasia (inability to express language) which includes halting speech
• repetitive speech (perseveration)
• disordered syntax and grammar and disordered structure of individual words

Research reviews

• Bauman and Kemper (2005) review neuroanatomical evidence that language impairments in autism may be related to abnormalities in Broca's area (PMID: 15749244).
• Anderson and colleagues (2009) review evidence of lower activity in Broca's area and Wernicke's area in high functioning individuals on the autism spectrum.
• Plaza and colleagues (2009)review a case study where a tumor prevented the use of Broca's area (PMID: 19274574).
• Amunts and Zilles (2012) review evidence of complex cytoarchitecture of the Broca's area, especially relating to interpreting and producing speech (PMID: 22763211).