Parkinson’s disease (PD) affects an estimated 1.5 million Americans and about 2% of people over 65 in the U.K. Its prevalence increases with age, although roughly 15% of Americans with Parkinson’s disease are 50 or younger. Parkinson’s disease is part of a broader spectrum of disorders known as parkinsonism. While it was viewed as fairly homogeneous in the past, researchers and clinicians now recognize the complexity of the disease and its related diseases.
The defining neurological marker of Parkinson’s disease is the destruction of the substantia nigra pars compacta, a small nucleus in the brain that is one of the major dopamine-producing brain areas. Symptoms of PD are not evident until around 80% of the neurons in the substantia nigra (literally translated as “black substance”) are destroyed. Because the substantia nigra produces dopamine, which is an important neurotransmitter, the depletion of dopamine in the brain that is associated with PD affects the striatum, which in part suppresses the subthalamic nucleus. This in turn results in more activity in the globus pallidus and substantia nigra pars reticulata, which in the end leads to more activation of the inhibitory thalamic nuclei that are involved in motor functioning. To summarize, decreased dopamine results in decreased motor activation as well as other motor problems.
The common features of Parkinson’s disease are easily remembered by the mnemonic TRAP.
- T – Tremor, specifically resting tremor. Tremor that occurs when moving (e.g., reaching for an object) is called essential tremor and is not a defining characteristic of PD; in fact, it is a different but related disorder.
- R – Rigidity. Difficulty moving and stiff arms and limbs.
- A – Akinesia. No or slow movements.
- P – Postural instability. Posture problems.
Gait abnormalities is also one of the common features of PD. It is especially useful for detecting the disease early in the process. The common gait problems are decrease height and length of step and less arm swing (i.e., walking more with a shuffle than a normal gait). People with PD also often take very small steps when turning around.
PD patients often have difficulty swallowing saliva so they often drool. They also often have micrography (very small writing) that progressively gets smaller with prolonged writing. Depression is common in PD patients as well. If given levodopa (L-dopa) they will respond. Symptoms of dementia often occur as well but they usually occur after a few years post diagnosis. However, there are often more mild cognitive changes early on in the disease process, such as slowed processing speed and slowed reaction time.
Reference
Approach to diagnosis of Parkinson disease (C. Frank, G. Pari, & J. P. Rossiter, 2006). Canadian Family Physician, 52, 862-868.
The man had committed a crime and was sentenced to pay. A crowd gathered to watch his punishment. There standing before him was the fateful Madame, the progeny of a French engineer. This Woman with the acerbic jaw was to seal the criminal’s fate. He faced the crowd wide-eyed and fearful, pleading for his life. His pleas seemed to fall on deaf ears as the frenzied crowd prepared for the spectacle. A German man stood waiting to play his part. Theodor Bischoff was not there to enjoy the public execution, he was there in the name of science. As the executioner led the criminal to the apparatus named after Joseph Guillotin (who by the way did not invent the guillotine), Bischoff approached. The blade fell and the criminal’s head dropped to the ground. Bischoff quickly rushed over to the head to perform his experiment.
This was not true but back in the day it seemed a very logical explanation, especially in light of the new discovery about how the heart worked like a pump for blood. The pineal gland was Descartes ideal structure where mind and body interacted because it was in the middle of the brain and was a singular brain structure (most structures in the brain are in both hemispheres. So for example, there are two hippocampi, two caudates, two frontal lobes, etc…). Even with Descartes advances, psychology remained a philosophy until the 1800s when Wundt and other empiricists created experimental psychological laboratories. From there, the field of psychology grew exponentially into the major field it is today.
As someone with a strong neurobiological foundation, I believe that the brain is the center of all behavior. What is the evidence for that belief? Remove someone’s brain and see if they have any behavior (note: I’m not endorsing this behavior, I’m merely postulating a hypothetical situation). Without the brain, there is no behavior. So, the brain is necessary for behavior but is it sufficient?