Brain Plasticity and functional recovery of the brain

What is plasticity? (synaptic pruning)

It refers to the brain’s ability to change and modify its own structure and function as a result of experience

During infancy and childhood, the brain experiences a rapid growth in the number of synaptic connections. As we grow, synaptic connections rarely used are deleted and frequently used ones are strengthened in a process called synaptic pruning.

What does ‘experience’ mean?

• Experience includes everything outside the body (e.g. driving a car, playing a musical instrument, etc.)

A01: Research conducted by Maguire/ Strength

• Maguire studied the brains of London taxi drivers. This was because taxi drivers complete a complex test called ‘The Knowledge’, which assesses their recall of the streets and routes. This makes them an ideal group for the study of spatial navigation

• Using MRI scans, Maguire found their hippocampus was significantly larger than a matched control group and there is an increased volume of grey matter was found in the posterior (rear) hippocampus

• They also found there was a positive correlation between the amount of time spent as a taxi driver and the volume in the posterior hippocampus.

• These results support brain plasticity and suggests experience such as driving a taxi, can change the structure of the brain, e.g, an enlarged hippocampus. It also implies frequently used neural pathways develop stronger connections.

A01 Meditation

What is functional recovery?

• The transfer of functions from a damaged area of the brain after trauma to other undamaged areas

• which allows the brain to recover its abilities and mental processes that have been compromised (due to brain injury or trauma)

What happens to the brain during recovery?

The brain can reorganise itself by forming new synaptic connections close to the damaged area

It can do this through a process term called neuronal unmasking where dormant synapses (which have not received enough input to be active) open connections to compensate for a nearby damaged area of the brain.

So secondary neural pathways which wouldn’t typically be used to carry out certain functions, are activated to continue functioning in the same or a similar way

• This process is supported by the many structural changes to the brain.

how does the brain structurally change?

• AXONAL SPROUTING → the growth of new nerve-endings that connect to other undamaged nerve cells to form new neuronal pathways

  • (this happens when an axon is damaged and it loses its connection with neighbouring neurons.)

• REFORMATION OF BLOOD VESSELS →

• RECRUITMENT OF HOMOLOGOUS (SIMILAR) AREAS ON THE OPPOSITE SIDE OF THE BRAIN TO PERFORM A SPECIFIC TASK → this means that specific tasks can still be performed, e.g, if the Broca’s area was damaged on the left side of the brain, the right-sided equivalent would carry out its functions and functionality may shift back to the left side over time.)

Practical application

• One limitation of functional recovery it doesn’t lead to a full recovery

• A few weeks after an injury or illness, spontaneous recovery tends to slow down, so a form of physical therapy may be required to continue improvements in functioning.

• For example, movement therapy and electrical stimulation of the brain may be needed to counter the deficits in motor and cognitive functioning, following a stroke.

• This shows that, although the brain has the capacity to recuperate itself, it still has its limits. So this process needs further intervention if it is to be completely successful.

• However, the idea of plasticity has improved our understanding of neurorehabilitation. It has allowed us to create therapies to minimise any damage and aid people to function normally as fast as possible.

Research support from animal studies

An advantage for plasticity is the early evidence from animal studies

Hubel and Wiesel sewed one eye of a kitten shut and analysed the brain’s cortical responses. They found that areas of the visual cortex, associated with the shut eye, continued to process information from the open eye.

This study displays that the brain can structurally change to compensate for damaged areas to allow functioning to continue.

Generalising animal research to humans

• However, Animal research into neuroplasticity and functional recovery can be criticised for extrapolation. 

• For example, Tajiri et al’s research used a sample of rats. Rats and humans are physiologically different so the effects of stem cells on the brains of rats may not be the same as the effects of stem cells on the brains of humans. 

• Furthermore, Hubel and Wiesel also conducted their study on an animal, a kitten. Since, the brains of humans and kittens are structurally different, it’s not accurate to assume the same results in humans.

• This is a weakness because, it means that research based on non-human animals cannot be generalised to humans and therefore it is difficult to draw firm conclusions.

One limitation of plasticity is that it may have some maladaptive behavioural consequences.

Evidence has shown that the brain’s adaptation to prolonged drug use leads to poorer cognitive functioning in later life, as well as increased risk of dementia (Medina et al)

Also 60-80% of amputees have been known to develop phantom limb syndrome, where they continued to experience sensations in the missing limb as if it was still there.

these sensations are usually unpleasant, painful and are thought to be due to cortical reorganisation in the somatosensory cortex that occurs as a result of limb loss

This suggest the brains ability to adapt may not always be beneficial.