Introduction to brain injury Flashcards
Causes of brain damage
There are several ways through which brain damage may occur
The cause of the damage has important implications for deficits and recovery
- acute brain damage (penetrating wound, stroke)
- cumulative brain damage (closed-head injury or diseases e.g., tumours)
Acute brain damage
- Strokes, trauma, and penetrating injuries
- Results in immediate loss of function, followed by a period of recovery.
Penetrating brain injury
- Causes an immediate effect of tissue death (but also causes other immediate effects such as bleeding)
- Bleeding may affect other areas of the brain, immune response to a foreign body (leading to swelling), a ‘clean-up’ of cell debris.
- These effects can cause acute symptoms as they impact on functioning.
- Can cause longer-term effects, which generally promote recovery e.g., reorganisation of blond supply – reorganisation of function of remaining neurons.
Cumulative brain damage
- Cumulative brain damage is the opposite of acute brain damage, cumulative damage will result in gradual effects that generally worsen over time for example, cancer.
Repeated traumatic brain injury.
- Often afflicts athletes playing contact sports over many years.
- May experience repeated concussions of various severity.
- The accumulation of these injuries leads to significant deficits (e.g., ‘punch drunk syndrome’)
“Punch-Drunk Syndrome’, also known as, dementia pugilistica or boxer’s syndrome is a chronic encephalopathy (CTE).
- This condition is common among boxers.
- It is caused by head trauma and the condition typically develops about 16 years after the initial head injury
- the boxers who suffer from this condition will commonly experience tremors, slowed movement, speech problems and confusion.
Transient damage/imbalance
- single concussion may affect functions related to consciousness, but its effects may be only transient
- imbalances in neurotransmitters/hormones also tend to be transient if their causes are external (e.g., diet)
- these can lead to mental health issues such as, depression, schizophrenia
Localised damage
- This refers to the death of cells in the region of injury.
- Here the vmPFC has been damaged by a stroke.
- Generally easy to identify (assuming there is a significant amount of damage)
Non-localised damage
- Difficult to identify because it is generally diffuse
- E.g., cell death can occur when neural input from a damaged region is no longer received.
- Reflects a damaged system as opposed to a damaged area.
Brain injury and Plasticity
- Brain injury has milder and shorter-lived effects if sustained in childhood (known as Kennard principle)
The Kennard principle
- States that the younger an organism is, the greater recovery from brain injury will be
- Describes the concept that the immature brain appears more resilient to injury compared with the term brain and can remap and reorganise more effectively to preserve function, and is thus more plastic
e.g., children with damage to Broca’s area can develop adult language abilities and children with hemispherectomies can develop relatively normal cognitive functions
However,
- Children with prefrontal injuries in infancy or early childhood have very poor outcomes
- Speech may survive early brain injury, but other cognitive functions may be impaired
Early Brain Lesions
Neurogenesis - the process by which new neurons are formed in the brain
In animals, injury during neurogenesis has good outcomes but injury during migration and cell differentiation is devastating
- When neurogenesis is still ongoing, damaged cells can be replaced by new ones
- Once the main period of neurogenesis ends, not enough new cells can be produced to replace those lost
Early Brain Lesions lead to systematic changes in later brain structure
- Changes in organisation of remaining, intact circuits
- Generation of new circuitry
- Generation of new neurons and glia
Factors that influence Plasticity:
- A wide range of factors beyond age can influence recovery
- A tactile stimulation, choline supplement, nicotine, neurotrophic factors
- Some can also impair recovery (e.g., reduction in hormone or neurotransmitter levels)
Case study: Broca’s patient “Tan” (1800)
- Broca provided the first “case study” of brain injury, and the first attempt to localise function, in the 1800s
- The patient could only repeat the word “tan” over and over
- Post-mortem showed they had damage in the frontal lobes (“Broca’s area”)
- This study was significant – lead to the concept of localisation of function (the idea that specific brain functions existed in some areas but not others)
- OTHER RESEARCHERS went on the localise other functions in similar ways for example, Wernicke’s area
Case study: Phineas Gage’s accident (1848)
Phineas Gage experienced traumatic brain injury when an iron rod was driven through his skull, destroying much of his frontal lobe
In a 1994 study, researchers used neuroimaging techniques to reconstruct Phineas Gage’s skull and determine the exact placement of the injury
- Their findings indicate that he suffered injuries to both left and right prefrontal cortices, which would result in problems with emotional processing and rational decision-making
- “He is fitful, irreverent, impatient of restraint of advice when it conflicts with his desires, at times pertinaciously obstinate, yet capricious and vacillating.”
- Impulsive, unsteady, showed a lack of respect, stubborn, unpredictable changes in mood and behaviour, can’t make up his mind about things
- In this regard, his mind was radically changed, so decidedly that his friends and acquaintances said he was “no longer Gage”.
- He is often reported as having lost his inhibitions- so that he started behaving inappropriately in social situations
- Some reports state that he became violent and uncontrollable
- Damage was later localised to the orbitofrontal cortex
Case study: H.M. (Henry Molaison, 1953)
Treatment for his epilepsy had been unsuccessful, so at the age of 27, HM agreed to undergo radical surgery that would remove the hippocampus.
Previous research suggested that this could help reduce his seizures but the impact it had on his memory was unexpected.
- H. M’s seizures decreased.
- H.M lost the ability to form new memories.
- This is called anterograde amnesia.
- He could do a task and even comment that it seemed easier than he expected, without realising that he had done that task a hundred times before.
- His anterograde procedural memory was completely affected.
Case study: DF
Patient DF is a woman with visual apperceptive agnosia who has been studied extensively due to the implications of her behaviour for the two streams theory of visual perception
- Though her vision remains intact, she has difficulty visually locating and identifying objects
- Unable to discriminate the width of objects
- Bilateral damage in ventral visual stream
- Has severe deficits in visual perception with relatively intact visually guided action
This supports the “two-stream” hypothesis of Milner and Goodale
(Goodale & Milner, 1992)
- Proposed that the distinction between vision-for-action and vision-for-perception can be mapped onto the two streams of visual projections arising from early visual areas in the primate cerebral cortex
- A dorsal stream projecting to the posterior parietal cortex and a ventral stream
Single vs Double dissociation
Single dissociation
- Finding a deficit in one behaviour but not another after damage to a particular brain region
- Suggests the affected area is responsible for the behaviour
- Can be done using either a case of group study
- E.g., early studies with case DF relied on single dissociations
Double dissociations
- Considered the ‘holy grail’ of neuropsychology
- Consider two brain areas (A and B) and two functions (X and Y):
If area A is damaged and function X is impaired (but Y is intact)
And when Area B is damaged, and Y is impaired (but X is intact)
- Area A is necessary for function X (and not Y) and B is necessary for function Y (and not X)
Rehabilitation
Three main goals:
1. Restoration of function
2. Development of compensatory techniques
3. Encouraging use of residual skills
Why is rehabilitation significant?
- Requires cooperation of patient (including acknowledgement of problem)
- Can be focused on language, motor, memory, or some combination of all of these
- Important goal is to improve the quality of life for the patient.
