About Brain Injury


What is an Acquired Brain Injury (ABI) ?

Acquired brain injury (ABI) includes a wide range of disorders and diseases affecting the brain, with onset after birth. While ABI can occur at all ages, beginning in the newborn period through adulthood, the majority of individuals who sustain an ABI are adults.  Individuals who sustain brain injuries may be referred to clinical specialists and rehabilitation professionals for evaluation and treatment.

Traumatic Brain Injury (TBI): Is externally-caused and the most common type of ABI. The leading cause of TBI is falls. Other mechanisms of injury include:

  • Motor vehicle-related events
  • Sports-related injury
  • Child abuse (e.g., Shaken Baby Syndrome)
  • Interpersonal violence and other intentional causes (e.g., suicide and homicide attempts by firearms)
  • Military combat (e.g., blast injuries associated with exposure to improvised explosive devices: IEDs).

Stroke: Represents the second leading cause of ABI. Most commonly, strokes occur in persons over the age of 65. However, approximately one-third of strokes are experienced by individuals under age 65, including children.

Infectious Disorders: Includes primary infections (i.e., meningitis; encephalitis) of the central nervous system (CNS), caused by bacterial, viral, parasitic and other infectious agents. The brain may also be secondarily affected by infections which originate outside the nervous system (e.g., HIV infection; Lyme Disease).

Metabolic Disorders: Refers to disorders, which may be related to systemic disease (e.g., liver disease) or other insults to the CNS, with the most common cause being anoxia (oxygen deprivation), which may occur in a variety of contexts (e.g., near drowning, cardiac events).

Brain Tumors (Neoplastic): This category includes primary tumors, which develop within the central nervous system (CNS). While some primary brain tumors are malignant and associated with compromised life expectancy, most individuals are diagnosed with benign brain tumors. Secondary tumors, which are more prevalent, represent metastases (spread) from a primary cancer outside the nervous system  (e.g., lung, colon).

Neurotoxic Disorders: Refers to ABI resulting from environmental or occupational exposure to known toxins, such as heavy metals (e.g., lead poisoning) and gases (e.g., carbon monoxide), as well as drug and alcohol use/misuse.

Neurodegenerative Disorders: Some acquired disorders are progressive and usually associated with a gradual decline in cognitive status (dementia) and functional capacity. Examples include:

  • Chronic Traumatic Encephalopathy (CTE), a neurodegenerative disorder associated with repetitive head impacts
  • Multi-Infarct Dementia (MID) associated with multiple strokes

Factors Affecting Recovery and Outcome

The factors which impact recovery and outcome in persons who experience an acquired brain injury are varied and complex. In addition to cause, these include:

  • Age at time of injury
  • The severity and the sites of injury within the brain
  • Duration of loss of consciousness
  • The occurrence and nature of complications
  • Gender
  • Race/Ethnicity
  • Pre-injury general health and functional status
  • Socioeconomic status and healthcare disparities (e.g., lack of health insurance; homelessness; untreated conditions, such as hypertension in persons who are at risk for stroke)
  • Access to and participation in rehabilitation
  • Access to community-based supports (e.g., case management)
  • Other risks (e.g., substance use disorder)

Consequences of Acquired Brain Injury

For each individual who experiences an acquired brain injury the acute and potential consequences vary, with respect to cause and other factors. The disorders and functional changes resulting from ABI require timely recognition and rehabilitation, as well as long-term supports and services, to facilitate optimal independent functioning and quality of life.

Common functional consequences associated with acquired brain injury, as well as clinical assessments to consider are included below:

Motor Disorders: Brain Injuries may affect areas of the brain that control movement which may result in:

  • Paralysis of voluntary movement caused by injury to the motor cortex (precentral gyrus) in the frontal lobe, or the descending pathway (pyramidal system) arising from that area, which may result in contralateral paralysis of movement  (i.e., paralysis on the opposite side of the body)
  • Extrapyramidal Disorders: Injury and diseases affecting other parts of the brain (e.g., cerebellum) may be associated with disturbances in the regulation and control of motor movements (e.g., tremor, incoordination)

Physical and Occupational Therapies are critical in addressing motor disorders associated with brain injuries in order to:

  • Facilitate ambulation and mobility
  • Optimize recovery of function and capacity for independently performing activities of daily living, or ADLs (e.g., bathing and other self-care)
  • Prevent secondary physical disabilities (e.g., muscle contractures; skin breakdown)
  • Evaluate individuals for adaptive equipment and mobility devices (e.g., wheelchair assessments; braces)

Orthopedics and Physiatry: For some individuals, assessment and treatment by an Orthopedic Surgeon, Physiatrist (physician who specializes in physical medicine and rehabilitation), or Osteopath (DO: Doctor of Osteopathic Medicine) may be needed. Interventions may include:

  • Treatment of fractures and other physical injuries
  • Serial casting to improve and maintain range of motion
  • Surgical intervention – e.g., implantation of a Baclofen pump to address muscle tightness and spasms (spasticity)
  • Treatment of chronic muscle pain

Assessment and treatment by a Speech and Language Pathologist (SLP) may be indicated for individuals who exhibit swallowing disorders (dysphagia).

Neurocognitive Disorders: Individuals who sustain a brain injury may experience neurocognitive changes related to the cause, as well as the sites and severity, of injury within the brain. While individuals who sustain moderate/severe acquired brain injury are at greater risk for exhibiting residual neurocognitive impairment, certain subpopulations of persons with ABI may exhibit mild cognitive deficits, which impact functioning and necessitate targeted assessment, including individuals who exhibit persistent post-concussion syndrome or symptoms which may be related to the cumulative effects of repeated head impacts (e.g., sports-related injuries) or other exposures (e.g., blast injuries sustained in military combat).

Clinical neuropsychological evaluation is the recommended approach for identifying, characterizing, and quantifying the neurocognitive disorders associated with acquired brain injury. A Clinical Neuropsychologist is a licensed psychologist, whose training and expertise are the assessment and rehabilitative treatment of individuals with neurological disorders. In addition to testing of general intellectual ability, neuropsychological evaluation includes assessment with respect to the following domains:

  • Attentional Capacity/Arousal including assessment of verbal and non-verbal attention span; mental tracking; and capacity for divided attention
  • Executive Skill including ability to establish, maintain and shift cognitive set; planning and sequencing; problem-solving skill; verbal and non-verbal reasoning; and social judgment
  • Constructional Skill including the ability to draw or assemble two and three-dimensional designs
  • Academic Skills including administration of tests of auditory and written math skills; spelling skill; reading and reading comprehension
  • Learning and Memory includes administration of verbal and non-verbal measures of immediate (short-term), working and long-term memory, as well as tests of verbal and non-verbal learning and recall, retrieval, and/or recognition

Individuals with ABI may exhibit a variety of memory disorders (amnestic disorders) including changes in the ability to:

  • Remember events experienced, or information learned, prior to sustaining brain injury (retrograde amnesia)
  • Learn new information following injury (anterograde amnesia)
  • Remember facts, concepts and symbols (semantic memory)
  • Remember one’s personal history (autobiographical memory)
  • Recall events or plans (episodic memory)
  • Remember temporally-ordered motor sequences or habits, such as dancing, driving, throwing a ball (procedural, or unconscious long-term memory). This type of memory is often preserved in persons with ABI.

Orientation includes an individual’s knowledge of general, personal, and temporal information, as well as orientation to home and neighborhood (topographical orientation) and direction (right-left orientation).

Perception includes performance on auditory, visual and tactile (haptic) tasks. Individuals with ABI may also exhibit disorders of complex processing, or agnosias, referring to the loss of the ability to recognize or comprehend objects that are seen or sounds that are heard. For example, individuals with prosopagnosia, a type of visual agnosia, are unable to recognize familiar faces or learn to recognize new faces.

Praxis, the ability to correctly execute motor commands and other purposeful actions, may be compromised in persons with brain injuries (i.e., dyspraxia)

Language and Communication: Injury to the left hemisphere (side) of the brain may result in aphasia or dysphasia, an acquired disorder of language and verbal output. There are several types of aphasia, which are classified as fluent (e.g., Wernicke’s aphasia) or non-fluent (e.g., Broca’s aphasia). Injury to the left side of the brain may also affect an individual’s ability to read (dyslexia) and spell words. Individuals who exhibit aphasia and other communication disorders necessitate evaluation by a Speech-Language Pathologist to inform appropriate rehabilitative interventions. A neuropsychological evaluation usually includes tests of language functions (i.e., verbal intelligence, verbal learning/memory), as well.

In addition to fluency, other qualities of verbal output may be affected by ABI, including impaired articulation (dysarthria) and abnormalities in the pitch, rhythm and melody of speech, referred to as dysprosodia. Difficulties with naming (anomia or dysnomia) and/or word retrieval is often experienced by individuals with ABI.

Cognitive Rehabilitation Therapy: Based upon comprehensive assessment of the acquired neurocognitive, communication, and cognitive-linguistic disorders associated with ABI, cognitive rehabilitation therapy may be recommended to promote recovery and to assist in developing appropriate compensatory strategies (e.g., compensatory memory strategies). Assistive technology devices may be utilized to address the neurocognitive and communication disorders associated with ABI, and to optimize performance of instrumental activities of daily living (IADL) tasks (e.g., adhering to prescribed medical directives and medications, such as insulin regimen and other aspects of diabetes management).

Neurobehavioral Disorders:  The same range and types of psychiatric disorders exhibited among the general population may also be diagnosed in persons who sustain a brain injury. Depression is one of the most common psychiatric disorders and response to having experienced an acquired brain injury, which in part may be correlated with the site(s) of injury to the brain (e.g., frontal lobe stroke). Mania and psychotic disorder, evidenced in hallucinations and delusions, are less commonly observed in persons with ABI.

Personality change, common among individuals who experience a traumatic brain injury, is associated with injury to the prefontal cortex (PFC) of the brain. The neurobehavioral symptoms associated with PFC injury, which are varied and related to the sites of injury within the prefrontal cortex, may include:

  • Diminished capacity for recognizing or anticipating the consequences of one’s own behavior, with respect to self or others
  • Disinhibition (e.g., impulsivity, aggression)
  • Difficulties initiating and maintaining goal-directed behavior, or making decisions  (abulia or apathy)
  • Sexual and social inappropriateness or intrusiveness
  • Irritability and difficulty regulating emotions

Individuals who sustain an ABI in certain psychologically-traumatizing circumstances (e.g., combat-related TBI) are at particular risk for developing Post Traumatic Stress Disorder (PTSD). The presence of a premorbid (i.e., prior to ABI) psychiatric or developmental disorder; predisposing genetic factors or family history of mental illness; and substance use disorder may complicate and/or increase the risk for developing a neuropsychiatric disorder in persons who have experienced an ABI.

Individuals who exhibit neurobehavioral/neuropsychiatric disorders associated with ABI necessitate evaluation and, when indicated, ongoing treatment by licensed mental health clinicians, who may include neuropsychologists, behavioral psychologists, or neuropsychiatrists. When undiagnosed and unaddressed, the neurobehavioral consequences of ABI can significantly impact an individual’s ability to participate in rehabilitation and functional outcome. In some instances, failure to address neuropsychiatric symptoms may place the individual with an ABI or others at risk (e.g., suicide attempt or aggression), including risk for institutionalization and incarceration.

Sensory Impairment: Brain injuries affecting the primary sensory areas and pathways within the brain may result in permanent sensory loss.

Sensory disorders may include:

  • Contralateral (opposite side of injury within the brain) loss of touch, vibration sense, perception of movement and the position of limbs and other body parts (i.e., conscious proprioception)
  • Blindness may result from injury to the retina or optic nerve (Cranial Nerve II: Optic Nerve), which partially crosses (decussates) in the brain. Injury to the nerve after it crosses, or injury to the visual (calcarine) cortex in the occipital lobe may result in visual field impairments, evidenced in loss of vision in the opposite (contralateral) half or quarter of the visual field. Common causes of visual field impairments include stroke and traumatic brain injury. Blindness, secondary to retinal hemorrhages, may also be a consequence of abusive head trauma (i.e., Shaken Baby Syndrome). Acquired loss of color vision (achromatopsia), usually caused by a stroke, may also be associated with ABI.
  • Hearing loss and other auditory disorders may occur as a result of damage to the auditory nerve (Cranial Nerve VIII: Vestibulocochlear Nerve), auditory pathway, or auditory area within the temporal lobe of the brain. Acquired hearing loss may be a consequence of abusive head trauma in infants and children, exposure to neurotoxins, brain infection or a brain stem tumor affecting CN VIII.
  • Anosmia, or the loss of sense of smell, is associated with injury to the olfactory nerve (Cranial Nerve I: Olfactory Nerve). A common cause of anosmia is traumatic brain injury.

Depending upon the nature of the sensory impairments associated with brain injury, clinical evaluation by several specialists may be recommended, including a Neurologist, Audiologist, or Neuro-ophthalmologist.

Other Disorders Associated with ABI: Other consequences of ABI may include seizures, chronic pain, sleep, and headache disorders. One of the most common co-occurring disorders exhibited by individuals who sustain ABI is substance use disorder.  Some individuals who sustain severe ABI fail to recover and exhibit persistent disorders of consciousness.

Brain Basics and Functional Neuroanatomy

What is the Central Nervous System?

The human central nervous system (CNS) includes the brain and spinal cord. The subsections of the brain, which are contained within the skull, include the:

Cerebral Hemispheres: The human brain has two cerebral hemispheres connected by the corpus callosum and other commissures. Each cerebral hemisphere includes the frontal, parietal, temporal, and occipital lobes. On the surface of the cerebral hemispheres are convolutions known as gyri (singular: gyrus), which are separated by spaces known as sulci (singular: sulcus) or fissures. 

Cerebral Hemispheres Diagrams

Within the gyri are the cell bodies of nerve cells (neurons), which constitute the cerebral cortex and are also referred to as the gray matter. Neurons give rise to fibers (axons) covered in a lipid substance, known as myelin. Neurons also have receptor processes known as dendrites.

Within the cerebral hemispheres, axons which may be carrying information (e.g., from motor neurons) to the spinal cord (descending pathways), and those fibers which ascend from the spinal cord and other structures (e.g., carrying sensory information) constitute the white matter. Axons facilitate functional connectivity within the CNS, and the connections between neurons, or synapses, are chemically mediated by neurotransmitters (e.g., dopamine). 

Basal Ganglia: These nuclei (group of cell bodies), located within the cerebral hemispheres, are part of the extrapyramidal system. The EPS is involved in the regulation and control of voluntary movement.

Diencephalon: is also part of the CNS and includes the thalamus, hypothalamus and epithalamus. The functions of the diencephalic structures include regulation of endocrine glands (e.g., thyroid); somatic functions (e.g., thirst, body temperature); sleep; emotion and behavior; and relay of sensory information to the cerebral hemispheres. 

Brain Stem: includes the midbrain, pons, and medulla, which is continuous with the spinal cord. In addition to the ascending and descending pathways, the brain stem includes nuclei which control the movement of the face, tongue and eyes, as well as sensory (e.g., taste, hearing) and extrapyramidal functions.

Cerebellum: is part of the extrapyramidal system and involved in the coordination, accuracy and timing of voluntary movement, including eye movement. Other functions of the cerebellum include gait, maintaining posture, and balance. The cerebellum also plays a role in cognition and the regulation of behavior.

Spinal Cord: is contained within the vertebral column, and includes ascending (sensory) and descending (motor) pathways. The spinal nerves, which are part of the peripheral nervous system (PNS), receive sensory information from the skin and other structures (e.g., joint capsules) and also provide motor innervation to muscles.