Plasticity and functional recovery of the brain after trauma

What is plasticity?

The brain’s tendency to change and adapt as a result of experience/new learning throughout life

What is synaptic pruning?

• During infancy, the brain experiences rapid growth in the number of synaptic connections - 15,000 per neurone in the first few years, double the adult brain.

• As we age, unused connections are deleted and freq used ones are strengthened.

What is the purpose of synaptic pruning?

Enables lifelong plasticity where new neural connections are formed in response to new demands on the brain

What was Maguire et al. (2000)’s research into plasticity?

• Found a significantly larger volume of grey matter in the posterior hippocampus in the brains of London taxi drivers than a control group.

• This part of the brain is associated with the development of spatial and navigational skills

• As a part of their training, they take a complex test which assess their recall of city streets and possible routes - Maguire found this alters their brain structures.

• Positive correlation: the longer a taxi driver was doing the job, the more pronounced the structural difference.

How does Draganski et al. (2006)’s research support Maguire?

• Imaged the brains of medical students 3 months before + after their final exams

• Found learning-induced changes occurred in the posterior hippocampus and the parietal cortex.

What evidence is there for plasticity being a lifelong ability?

• Bezzola et al. (2012) used fMRI to show that 40 hours of gold training produced changes in the neural representation of movement in 40-60 year olds.

• The researchers observed increased motor cortex activity in the golfers compared to a control group

What are the negative behavioural consequences of plasticity?

• Medina et al. (2007) suggests the brain’s adaptation to prolonged drug use leads to poorer cognitive function in later life + increased risk of dementia.

• Ramachandran and Hirstein (1998) believe that the majority of amputees experience phantom limb syndrome because of the cortical reorganisation in the somatosensory cortex.

• Suggests the brain’s ability to adapt isn’t always beneficial.

What is functional recovery?

• Form of plasticity

• Following a trauma, the brain has the ability to redistribute/transfer functions performed by a damaged area to an undamaged.

How does recovery work?

• Spontaneous recovery - process occurs quickly after the trauma

• Slows down after several weeks/months

• Rehabilitative therapy may further recovery

What happens to the brain during recovery?

• Brain forms new synaptic connections around the damaged area

• Secondary neural pathways that would not be typically used to carry out certain functions are activated to continue function.

What is atonal sprouting?

Growth of new nerve endings which connect with other undamaged nerve cells - forms new neuronal pathways

What is denervation supersensitivity?

Axons that have similar roles become more aroused to compensate for those that are lost.

What is the negative consequences of denervation supersensitivity?

Oversensitivity in response to pain

What is recruitment of homologous areas?

• When one side of the brain cannot perform a certain task, the equivalent on the other side will carry it out

• Functionality then switches between the two sides after a time

How does functional recovery have real application?

• Understanding the processes of plasticity has contributed to neurorehabilitation

• Axonal growth encourages new therapies, eg constraint-induced movement therapy, used with stroke patients → repeatedly using the affected part of their body whilst the unaffected part is restrained.

How does amount of education influence recovery rate?

• Schneider et al. (2014) shows that the longer those with brain injuries spent in education, the greater their chances of a disability-free recovery.

• 40% who achieved DFR had 16+ years of education, compared to 10% who had less than 12.

How does functional recovery encourage research for new treatments?

• Banerjee et al. (2014) treated people who had total anterior circulation stroke with stem cells.

• They all recovered, compared to the usual 4% recovery

• However, the group was only 5 participants, and no control group.