Although medical treatment and physical rehabilitation help in the recovery of stroke survivors, a stroke often leaves a lasting mark. Depending on the location and extent of the damage, it may cause moderate to severe disabilities.
The brain is a complex structure which can be divided into 3 sections: the forebrain, the midbrain and the hindbrain. Damage to each of these areas results in different types of disabilities.
Stroke in the Forebrain
Some of the major functions of the forebrain are receiving and processing sensory information, thinking, creating and understanding language, perceiving, and controlling motor function.
The forebrain can be divided into two structures: the diencephalon and the telencephalon.
- The diencephalon is composed of the thalamus and the hypothalamus which are responsible for functions such as motor control, autonomic functions and relaying sensory information.
- The telencephalon is made up of the largest part of the brain, the cerebral cortex (or cerebrum). The cerebrum is divided in four lobes: the frontal, parietal, occipital and temporal lobe.
It is associated with higher level cognitive functions like reasoning and judgment. This lobe also contains important cortical areas which are responsible for voluntary control of muscle movement including those responsible for the production of speech and swallowing. Broca’s area is a part of the frontal lobe which is necessary for the coordination or programming of motor movements for the production of speech sounds. It is also involved in syntax which involves morphology (the allomorphs at the ends of words) and the ordering of words. The frontal lobe is also a significant part of the brain dealing with emotions, problem solving, reasoning, and planning.
When a stroke affects the frontal lobe, the following deficits can be expected:
- Broca’s aphasia or expressive aphasia (difficulty conveying thoughts through speech or writing)
- Apraxia (altered voluntary movements)
- Confusion, disorganized thinking
- Altered reasoning and judgment
- Hemiplegia (one-sided paralysis)
- Dysphagia (difficulty in swallowing)
- Clinical depression
The parietal lobe is located behind the frontal lobe.
It is primarily associated with sensation, including the sense of touch, kinesthesia, vibration and feeling of warmth and cold. This part of the brain is involved in controlling functions like recognition, orientation, movement, and perception of stimuli. It is also involved in reading and some aspects of writing.
When a stroke happens, the following conditions can be expected:
- Hemineglect (one-sided inability to respond to objects or sensory stimuli)
- Paresthesia (numbness, sensation of tingling in paralyzed or weakened limbs)
- Anomia (difficulty with word-finding or naming)
- Alexia with agraphia (difficulties with reading and writing)
- Finger agnosia (lack of sensory ability to identify which finger is which)
- Acalcula (difficulties with arithmetic)
- Left-right disorientation (inability to distinguish right from left)
The occipital lobe is located at the most posterior portion of the brain and is mainly involved in vision. The primary visual area receives the input while the secondary visual area integrates the input and gives meaning to it.
When a stroke occurs, the following conditions can be expected:
- Visual field deficit, or VFD
- Blind spots in the visual field or total blindness
- Visual agnosia (can see visual stimuli but cannot associate them with any meaning or identify their function)
The temporal lobe is located in front of the occipital lobe.
It is responsible for memory, auditory processing and olfaction and has also important functions in semantics or word meaning. Wernicke’s area is an important component of this lobe. Wernicke’s area is responsible for the ability to understand and produce meaningful speech.
When a stroke attacks the following conditions can be expected:
- Hearing difficulties
- Memory deficit
- Anosognosia (inability to recognize physical impairments after a stroke attack)
- Wernicke’s aphasia or receptive aphasia (language disorder that impacts language comprehension and the production of meaningful language)
Stroke in the Midbrain
The midbrain, or mesencephalon, is situated behind the frontal lobe and in the middle of the entire brain. It is mainly involved in functions such as vision, hearing and body and eye movements. Portions of the midbrain which are called the red nucleus and the substantia nigra are involved in body movement control.
If a stroke strikes, the following symptoms are expected from the patient:
- Visual field deficit, or VFD
- Hearing impairment
- Uncoordinated body movement
- Involuntary eye movement
Stroke in the Hindbrain
The hindbrain (rhombencephalon) is the posterior part of the brain and is composed of:
– The cerebellum
– The pons
– The medulla
The midbrain, pons and medullas are collectively referred to as the brain stem together with the 12 cranial nerves
The cerebellum plays a very crucial part in maintaining balance and equilibrium, coordinating muscle movement and conduction of sensory information. It does not initiate movement but it contributes to movement precision and accurate timing.
Damage to the cerebellum during stroke attack includes:
- Ataxia (inability to coordinate movement)
- Difficulties in speed
- Gait impairments and problems with leg coordination
- Vertigo and disequilibrium
The Pons is located just above the medulla and below the midbrain.
It relays signals from the forebrain to the cerebellum and deals primarily with breathing, sleep, swallowing, bladder control, hearing, tastes, equilibrium, posture, eye movement, facial expressions and facial sensation. Inside it is the pneumotaxic center which regulates the change from inspiration to expiration.
The resulting damage to the pons during stroke attack includes:
- Alteration of smell, taste, hearing, or vision (total or partial)
- Urinary incontinence
- Drooping of eyelid (ptosis) and weakness of ocular muscles
- Decreased reflexes: swallow, gag and pupil reactivity to light
- Decreased sensation and muscle weakness of the face
- Weakness in tongue
- Nystagmus (involuntary eye movement)
- Alteration of breathing pattern
The medulla rhythmically stimulates the intercostal muscles and diaphragm, regulates heartbeat and regulates the diameter of arterioles thus adjusting blood flow. It also includes autonomic function such as vomiting and digestion.
Damage to the medulla during stroke attack includes:
- Loss of bowel control and constipation
- Alteration of heart rate
- Alteration of breathing pattern
- Blood pressure changes