I recently presented in Orange County, California the topic of “The Relationship of Age at Time of Injury to Neuropsychological Performance” and I shared that while there are many established research findings on brain-behavior as it relates to injury, this particular organ is very complex and unpredictable. Nevertheless, I wish to share some general theories about brain behavior and how it is able to reorganize; what is sometimes referred to as neural plasticity.
In short, neural plasticity refers to the idea that the brain, is able to reorganize itself, structurally and functionally, in response to injury or life events. It is believed by researches that brain damage that is sustained early in life may be less debilitating than brain injury experienced later in life as there may be mechanisms that allow for the more immature brain to reorganize. Interestingly, preterm infants continue to experience a high degree of debilitating neurodevelopmental difficulties, even when there is a progressive improvement. This is known as the Kennard Principle.
The crowding Hypothesis is based on the observation that individuals with left hemisphere brain injury experience a reorganization of language functions to the right hemisphere, which is typically considered to process nonverbal cognitive functions in an undamaged brain. Similar processes are described by the theory of Equiontentiality which notes that the brain has the capacity to transfer functional memory from the damaged portion of the brain to the undamaged portions of the brain. Lastly, Hebb’s Early Vulnerability Theory suggests that the immature brain is not able to compensate for an injury. It is therefore believed that brain injury in early development has a less specific effect and a more generalized effect on functioning. Longitudinal studies support functional recovery but with a pattern of deficits over time.
SO WHAT DOES THIS REALLY MEAN?
1. While there is evidence of adaptation of the developing brain when a brain injury has occurred, certain regions of the brain that have become damaged may not develop normally and intellectual capacity may become more apparent over time, which may be due to the brain’s processing capacities being affected.
2. With an injury, language acquisition in early development experiences a delay, regardless of left or right hemisphere injury.
3. In older children and adolescents, the severity of the injury is the major determinant of the sequelae at the time of injury and over time.
AREAS OF FUNCTIONING - LANGUAGE
Language development is heavily influenced by age. The greatest impairments with language are reported for infants under one year of age. From one to five years of age, there is a degree of sparing and some organization occurs to accommodate the development of language. Past five years, there is limited reorganization Rasmussen and Milner (1971) investigated left hemisphere injury early in life and found that language functions can be transferred to the right hemisphere from the left hemisphere. Overall, many children with left hemisphere unilateral lesions exhibited disorders in speech, writing, or calculation. In comparison, to the adult population, left hemisphere damage was found to be shorter in duration. Also, while adults with injury to the left hemisphere demonstrated severe and contrasting evidence of impairment across all measures, none of the deviations are observed in the children with unilateral injury (Bates 2001).
AREAS OF FUNCTIONING - MEMORY
Children with brain injury are less likely to exhibit deficits with implicit memory when compared to explicit memory Children with moderate to severe injury are more likely to show prospective memory deficits (remembering to perform an action). With adults, the impairment of memory is marked by deficits in both retrievals of previously acquired knowledge and the creation of new memory traces. Long term memory is often less impaired than short term memory.
Barrash, et al, (2011) found that adults with focal lesions in the ventromedial prefrontal cortex (vmPFC) of the brain had significantly more disturbed social behavior and executive/decision-making deficits, diminished motivation/hypo-emotionality and distress when compared to individuals with focal lesions in other areas of the brain. Lesions in the orbitofrontal area of the prefrontal lobe exhibit major antisocial behaviors such as disinhibition, emotional lability, and impulsivity. Seizures of the temporal lobe can also have significant effects on an individual's personality. For example, temporal lobe epilepsy can cause perseverative speech, paranoia and aggressive rages. Severe damage to the temporal lobes can also alter sexual behavior (e.g. increase in activity). With children, conduct problems such as Oppositional Defiance Disorder and symptoms associated with ADHD were the most prevalent of personality disturbance.