Stroke Impact: Multiple Hemispheres And Recovery

A stroke occurs when the brain's blood supply is interrupted, preventing an area from receiving enough oxygen-rich blood. This can be caused by a clogged or burst artery. As a result, brain cells begin to die, leading to tissue damage and loss of function. The effects of a stroke depend on its location and severity, as each part of the brain controls different functions. While strokes typically affect one hemisphere, it is possible for multiple hemispheres to be impacted, resulting in a wider range of side effects.

Left Hemisphere vs Right Hemisphere

The brain is divided into two halves, or hemispheres, each containing four lobes. Each hemisphere controls the opposite side of the body. For example, the left hemisphere controls the right side of the body, and vice versa.

A stroke occurs when the supply of blood to the brain is compromised, causing brain tissue to die. The effects of a stroke depend on where in the brain it occurs. All areas of the brain can be affected by a stroke, and every stroke will have unique effects. However, there are some general patterns that can be observed when looking at the left and right hemispheres of the brain.

Left Hemisphere

The left hemisphere controls movement on the right side of the body. A stroke in this hemisphere will usually result in motor impairments on the right side. Other effects may include:

• Weakness or paralysis on the right side of the body
• Sensory changes on the right side of the body
• Speech and language problems (aphasia)
• Problems with thinking and memory
• Behaviour changes, such as becoming more cautious and hesitant
• Impaired ability to read, write, and learn new information
• Problems with math, organization, reasoning, and analysis

Right Hemisphere

The right hemisphere controls movement on the left side of the body. A stroke in this hemisphere will usually cause motor impairments on the left side. Other effects may include:

• Weakness or paralysis and sensory loss on the left side of the body
• Left-sided neglect or lack of awareness of the left side
• Vision problems, including loss of the left field of vision in both eyes
• Problems with depth perception or directions
• Difficulty locating or recognizing body parts or objects
• Behaviour changes, such as lack of concern, impulsivity, and inappropriate words or actions

Multiple Hemispheres

When a stroke impacts both hemispheres, it is possible to experience motor changes and other effects on both sides of the body.

Bilateral Stroke

A bilateral stroke occurs when both hemispheres of the brain are affected. The brain is divided into two halves, or hemispheres, with each hemisphere controlling movement on the opposite side of the body. For example, a left hemisphere stroke will usually cause motor impairments on the right side of the body, and a right hemisphere stroke will likely impair movement on the left side. When a stroke impacts both hemispheres, it is possible to experience motor changes on both sides of the body.

The effects of a stroke depend on its location and the extent of the damage to the brain tissue. The brain is extremely complex, and each part has a specific function or ability. When an area of the brain is damaged by a stroke, the body functions it controls may be lost, resulting in disability or even death.

A stroke occurs when the supply of blood to the brain is interrupted, causing brain tissue to die due to a lack of oxygen-rich blood. This can happen when a blood clot obstructs an artery (ischemic stroke) or when an artery in the brain bursts and bleeds (hemorrhagic stroke).

Another case study describes a 47-year-old woman with hypertension who presented to the emergency department with altered mental status and was found to have massive frontal and parietal cerebral infarcts with radiological evidence of moyamoya disease, a rare progressive cerebrovascular disease.

In summary, a bilateral stroke occurs when both hemispheres of the brain are affected, potentially resulting in motor changes and other disabilities on both sides of the body. The effects of a stroke depend on its location and severity, and timely emergency care is critical to minimize tissue damage and improve outcomes. While some strokes can be treated with medication, others may require surgical intervention.

Parietal Lobe Stroke

A parietal lobe stroke occurs when there is a blockage or rupture of a blood vessel in the brain, which results in a lack of constant blood flow to the parietal lobe. This deprives the area of adequate oxygen and causes cell death, impairing sensory, visual, and/or language functions—sometimes permanently. The parietal lobe is located in the middle of the cerebral cortex, directly behind the frontal lobe, and is responsible for processing information from the senses, such as pain, touch, vibration, and proprioception (position awareness).

The effects of a parietal lobe stroke depend on which hemisphere is affected and the location and size of the injury. The brain is divided into two main halves or hemispheres, with the left hemisphere typically serving as the language center and the right hemisphere responsible for cognition, calculation, and spatial orientation.

A right-sided parietal lobe stroke may result in:

• Abnormal sensations (paresthesia) on the left side of the body
• Inability to see out of the lower left quadrant of each eye (inferior quadrantanopia)
• Spatial disorientation, including problems with depth perception and navigating
• Inability to recognize objects or the left side of one's own body (hemiagnosia or "alien hand syndrome")
• Loss of proprioception, causing misjudgment in movement and balance
• Lack of awareness or concern about the left-sided impairment (hemispatial neglect)
• Impulsive, manic, or inappropriate behaviours

On the other hand, a left-sided parietal lobe stroke may lead to:

• Right-sided weakness
• Paresthesia on the right side of the body
• Inability to see out of the lower right quadrant of each eye
• Difficulty with speech or language comprehension (aphasia)
• Problems with simple mathematics
• Impaired ability to read, write, and learn new information
• Lack of awareness that a stroke occurred (anosognosia)
• Cautious or hesitant behaviours

Regardless of the affected hemisphere, a parietal lobe stroke can also result in astereognosis, a sensory disorder where one cannot identify objects by touch.

The impact of a parietal lobe stroke is often more significant in the elderly, who may already be facing cognitive, sensory, and movement challenges. Delirium, characterised by confused thinking and reduced awareness, is a common complication in older individuals with this type of stroke.

While the loss of sensory function in a parietal lobe stroke allows for a faster recovery of motor skills with physical therapy, speech and language impairments can be more challenging to overcome and may require intensive speech therapy.

Hemiplegia

The most common cause of hemiplegia is vascular conditions, which include strokes, aneurysms, and cerebral haemorrhages. Traumatic causes, such as cerebral lacerations, spinal cord lacerations, and subdural hematomas, are also frequent. Infections of the nervous system, such as encephalitis, meningitis, and brain abscesses, can also lead to hemiplegia, as can malignancies, and demyelinating diseases of the central nervous system, such as multiple sclerosis.

The main clinical manifestation of hemiplegia is the severe or complete loss of motor function on only one side of the body. Sensation can also be lost completely or partially on the affected side. Further signs and symptoms vary between individuals and depend on the severity of each case. Usually, both gross and fine motor skills are affected. Less frequently, individuals may experience difficulty speaking (often characterised as slurred speech), difficulty swallowing, and trouble breathing.

Treatment of hemiplegia involves a multidisciplinary approach, including physicians, physical therapists, occupational therapists, and psychologists. The goal is to improve sensation and motor abilities so that individuals can perform their daily activities with as much independence as possible, as well as treating any underlying pathology causing the hemiplegia. This may include medication, surgery, and neuromuscular electrical stimulation.

Hemiparesis

The severity and location of a stroke will determine the location and extent of hemiparesis. For example, a stroke on the left side of the brain will result in right-sided weakness, while a stroke on the right side will cause weakness on the left side. This is because each hemisphere of the brain controls the movement of the opposite side of the body.

Treatment for hemiparesis typically involves rehabilitation with a physiatrist, physical therapist, and/or occupational therapist. Modified constraint-induced therapy (mCIT), electrical stimulation, cortical stimulation, mental imagery, and assistive devices are all methods that can help improve nerve function and increase strength and movement on the affected side.

The prognosis for hemiparesis varies from person to person, as every brain is wired differently and every stroke impacts different neural pathways. In some cases, hemiparesis may last for a few months, while in others it may persist for years or become a chronic condition. The brain's ability to heal and form new neural connections through neuroplasticity plays a crucial role in recovery.

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