Parkinson's Disease

• A neurodegenerative disease that affects the neurons in the substantia nigra (an area of the brain)
• The neurons in the substanti nigra produce dopamine, which is a neurotransmitter
• Dopamine is responsible for carrying messages between neurons to ensure effective planning, initiation and maintainence of movements 
• A person with Parkinson's will hae fewer neurons in the substantia nigra, which means less dopamine is produced
• Less dopamine being produced means the brain receives fewer or irregular messages about how to control movemen
• This is the reason people with Parkinson's have common motor symptoms (uncontrollable shaking) 

Tremors 

• Continuous, involuntary shaking or trembling of the body (not present in all cases of Parkinson's)
• Most tremors are 'resting tremors' (tremors that occur when the limb is not in use)
• Sometimes 'action tremors' (tremors that occur when starting some sort of motor activity) are experienced 
• 'Restless legs' (legs feel as if they are constantly moving especially at night) is also a common symptom of Parkinson's 
• Usually tremors are worst at rest, improve during voluntary movement and disappear during sleep 

Muscle Rigidity (Stiff Muscles)

• Muscles are tight and unable to relax even when resting
• Muscles won't do what people want them to do 
• Parkinson's sufferers have difficulty performing automatic movements (such as swinging their arms while walking or rolling over in bed)
• Muscle rigidity can also lead to a lack of facial expression through loss of facial muscle tone

Slowness of Movement (Bradykinesia)

• Movement is slow especially when initiating or executing movements and in performing repetitive movements
• This inolves a decrease in fine motor coordination required for 'delicate' work with hands (movements such as doing up buttons, putting on makeup and slicing vegetables)
• People with Parkinson's also have difficulty turning over in bed and it is common for their handwriting to become slow and small
• Bradykinesia impacts everyday activities and this is why it's one of the most disabling symptoms 

Posture Instability 

• Balancing and walking problems occur later in the course of the disease 
• Parkinson's sufferers with this symptom take short, shuffling steps and also have an inability to maintain a steady, upright posture 
• This symptom also makes individual's unable to prevent themselves from falling (a light shove is able to make them fall)  

Other Symptoms

• Due to the slow onset of Parkinson's it can take a while for individuals to notice the symptoms and realise they are suffering from them
• The severity of the symptoms vary from day to day and at different times throughout the day

• Swedish doctor Arvid Carlsson administered reserpine (a drug that would decrease the level of dopamine in the brain) to rabbits 
• The rabbits' movements became significantly impaired and very lethargic, similar to the movements of individual's suffering from Parkinson's 
• He also found out that he could restore the rabbits' movements to their original state by administering levodopa (a chemical that is converted to dopamine by neurons)
• Consequently levodopa (L-dopa) was the first treatment for Parkinson's disease

• Structural and functional neuroimaging techniques have enhanced the understanding of mental processes and areas of the brain involved in Parkinson's
• Neuroimaging has also been conducted on animals, mostly monkeys

CAT and MRI Scans

• CAT and MRI scans provide detailed images of degeneration in the brain
• This is useful for diagnostic purposes (assessing the extent of damage to the brain) and monitoring the degeneration of over time
• Images can be taken at a neuronal level within dopamin-producing areas and neural pathways where dopamine is used
• However CAT and MRI scans don't show the actual activity of the brain because they are still images

PET and fMRI Scans

• PET and fMRI scans are the preferred neuroimaging techniques because they provide detailed images of both brain structure and activity 
• Researchers can use these neuroimaging techniques in very precise ways (measuring the changes in the relase of dopamine and observing the impact in dopamine pathways)
• Brain activity in dopamin-producing and motor areas can also be viewed throughout at the same time
• fMRI scans have enabled earlier diagnosis of Parkinson's because of its detailed images at a neuronal level, more detailed monitoring of the rate of progression of Parkinson's and the impact of different treatments
• PET and fMRI scans also enable researchers to study changes in mental processes (cognitive function and impairments in social behaviour or personality) of people with Parkinson's 

There have been lots of studies on Parkinson's using neuroimaging techniques, these studies have investigated and enhanced the understanding of: 

• Brain functionality and processes underlying different motor symptoms 
• Consequences of reduced dopamine levels on non- motor mental processes and behaviour
• Non-motor symptoms of the disease that may precede the motor symptoms and provide evidence of onset 
• Activity in specific areas of the motor cortex associated with different symptoms such as hand tremors and rigidity the impact of different treatments, particularly medications (effects of various dosages and frequency of use, age-related differences in responsiveness etc)  
• The effects of gene therapies that may slow the disease’s progression and avoid side effects of existing treatments e.g. insert copies of a gene that may minimise dopamine depletion 
• New ways of compensating for the loss of neurons (implant fetal stem cells in the brains of individuals with Parkinson’s disease to establish new, healthy connections where dopamine may be released and thereby minimise the symptoms or their effects)