Neuroplasticity: Brain's Ability to Change

Neuroplasticity

• The brain can change and reorganize itself by forming new neural connections due to environmental demands

Mechanisms of Neuroplasticity

• Dendritic branching involves the growth of new dendrites in response to learning
• Synaptic pruning is the elimination of unused synapses to make neural networks more efficient
• Long-term potentiation (LTP) strengthens synaptic connections through repeated stimulation, improving learning and memory and primarily occurs in the hippocampus
• LTP creates structural changes, such as new dendritic spine growth

Draganski Study

• Used brain scans to demonstrate that learning new skills can change brain structure
• Participants who practiced juggling for three months showed increased gray matter in visual and motor areas
• After stopping the practice, these changes were partially reversed
• This is evidence of neuroplasticity, which shows the brain adapts structurally to learning and experience

Neurotransmission

• Neurons communicate through an electrochemical process involving an electrical impulse traveling down the axon
• This triggers the release of neurotransmitters across the synapse between neurons
• Neurotransmitters travel across this gap, binding to receptors on the next neuron
• This triggers an electrical impulse and communicates messages through the brain

Neurotransmitters

• They are signaling molecules released by a neuron that affect another cell, which may be another neuron, gland, or cell

Acetylcholine

• It is a neurotransmitter involved in memory, learning, and muscle movement
• It plays a major part in memory formation and synaptic plasticity, especially in the hippocampus
• Higher levels improve memory encoding and recall
• Lower levels are linked to memory impairment

Antonova et al. Study

• Targeted the role of acetylcholine in spatial memory
• 20 healthy male adults were randomly assigned to scopolamine or a placebo
• Played a virtual reality maze task with fMRI scans being recorded
• The participants navigated an arena to reach a pole, and the screen went black
• Participants then had to find the pole from the new position
• The scopolamine group performed worse and had reduced hippocampal activation
• Acetylcholine plays a role in encoding spatial memories
• The action is reduced in the hippocampus when blocked

Diathesis-Stress Model

• Genes are DNA segments coding for traits and influence behavior
• They do this by shaping brain structure, neurotransmitters, and hormone regulation
• "Diathesis" means predisposition
• The model suggests that genetic vulnerability interacts with environmental stressors to trigger conditions, like depression
• The 5HTT gene regulates serotonin transport
• Variations affect emotional resilience
• Shorter alleles are linked to a higher risk of depression under stress

Depression

• It is a mood disorder with persistent sadness, loss of interest, fatigue, and cognitive difficulties
• It affects emotions, thoughts, and physical health
• Serotonin is a neurotransmitter that regulates mood, sleep, and stress response
• Low levels of serotonin lead to depression, and contribute to emotional instability

Caspi et al. Study

• Examined the interaction between genetics and environment in depression
• Focused on the 5HTT gene, which influences serotonin transport
• Followed 847 New Zealand adults from birth
• Analysed participants' 5HTT gene variants (short/short, short/long, long/long) and exposure to stressful life events
• Individuals with one or two short alleles of the 5HTT gene were more likely to develop depression after multiple stressful events
• Those with two long alleles were more resilient
• Having the short allele increased vulnerability instead of directly causing depression

Hormones

• They are chemical messengers released by endocrine glands into the bloodstream, influencing behavior and bodily functions
• Hormones travel through the bloodstream acting slowly, unlike neurotransmitters which act rapidly in synapses
• Hormones influence mood, stress, memory, growth, and metabolism
• Target organs receive signals and messages

Cortisol

• It is a stress hormone released by the adrenal glands in response to stress functions
• It restores homeostasis, and regulates metabolism, immune response, and memory formation
• High levels of cortisol impair memory retrieval, especially when under long-term chronic stress

Newcomer et al. Study

• Targeted how cortisol affects verbal declarative memory
• 51 healthy adults were split into three groups (high cortisol dose, low cortisol dose, and placebo)
• Baseline tests were conducted before they were given tablets
• They took the verbal memory tests learning paragraphs each day
• Tested on the sixth days for long-term effects
• The high cortisol group performed worse on memory tasks
• The low cortisol group performed similarly to the placebo group
• High cortisol levels impair memory recall, while moderate cortisol has no significant effect

Brain Imaging Techniques

• These are scientific methods used to study brain structure and function through various types of scans
• They allow scientists to study the living brain, which records its structure, activity, and localization of function non-invasively

MRI

• An MRI is a brain imaging technique using magnetic fields and radio waves to create detailed images of brain structure
• Magnetic fields align hydrogen atoms in water molecules in the brain
• Radio waves disrupt this alignment and signals are measured to create a 3D image of the brain
• Static images of brain structure can be produced
• FMRI (functional MRI) shows real-time brain activity by measuring changes in oxygen levels in blood flow

PET Scan

• PET scans use radioactive glucose injected into the blood to record activity levels in the brain and measures the radioactive glucose metabolism in different regions

Maguire et al. Study

• Searched for whether extensive spatial navigation experience leads to structural brain changes in the hippocampus
• There were 16 male London taxi drivers and 50 male non-taxi drivers.
• VBM to measure hippocampal gray matter volume and pixel counting to reveal area
• The MRI found taxi drivers had larger posterior hippocampi and smaller anterior hippocampi with non-taxi drivers
• Showed the longer they worked as taxi drivers, the larger their posterior hippocampus was
• This shows MRI can find evidence to support neuroplasticity and extensive spatial navigation leads to structural changes in the hippocampus

Localization of Brain Function

• States specific parts of the brain are responsible for particular cognitive functions and behaviors

Strict Localization

• One area is solely responsible for a function

Relative Localization

• States functions are distributed across multiple areas

Function of Hippocampus

• The hippocampus is crucial for converting short-term memories into long-term declarative memories and spatial navigation

Patient H.M.

• H.M. had severe epilepsy and underwent surgery to remove his medial temporal lobes, which included the majority of his hippocampus
• H.M. had anterograde amnesia and could not form new declarative memories
• He also had partial retrograde amnesia, where he was unable to recall recent past long-term memories, but could remember his childhood memories
• The hippocampus is a temporary store of declarative memory
• H.M. retained procedural memory, so it is not localized to the hippocampus
• He could hold a conversation and repeat numbers, which shows short-term memory is retained

Conclusions

• Hippocampus is essential for forming declarative memories, but not for retrieving old ones
• The hippocampus is a temporary store of memory
• The hippocampus is not involved in procedural or short-term memory
• Different types of memory rely on separate brain structures