PSY 340 Week 3 Sensation, Perception and Movement Example

A Lost Sense of Smell and a Slowing Step: Sensation, Perception and Movement in Parkinson's Disease

[Student Name]

University of Phoenix

PSY/340: Biological Foundations in Psychology

Week 3 Assignment

[Instructor Name]

[Date]

The person described is a composite written for a model paper; research findings come from the sources listed.

The brain takes in information through the senses and acts on the world through movement. Both depend on precise pathways, and disease can disrupt them in revealing ways. This paper explains how sensation becomes perception and how the brain controls movement, using Parkinson's disease as a case that affects both.

The Case

Walter is sixty-three and retired after thirty years as a mail carrier in Prescott Valley, Arizona. About eight years ago, his wife noticed he no longer commented on the smell of dinner, and he admitted that coffee and wood smoke had faded for him. He thought nothing of it. Two years ago, his left hand began to shake when resting on his knee. His handwriting has become small and cramped, he takes short, shuffling steps and his face shows less expression than it used to. A neurologist diagnosed Parkinson's disease.

Sensation: Detecting the World

Sensation begins with transduction, the conversion of physical energy into neural signals by specialized receptors. Light is transduced by photoreceptors in the retina, sound by hair cells in the inner ear and odors by receptors on olfactory neurons high in the nasal cavity. Each odor molecule binds to a subset of hundreds of receptor types, creating a pattern that the brain reads as a particular smell.

Olfaction is unusual among the senses. Signals travel from the olfactory bulb directly to areas of the temporal lobe and limbic system, without first passing through the thalamus, which helps explain why smells can trigger vivid memories and emotions.

Perception: Building a Picture

Perception is the work of organizing those signals and making sense of them. In the 1950s, little was known about how the cortex carried out that work. Hubel and Wiesel (1962) recorded from single cells in the visual cortex of cats while showing them simple patterns of light. They found cells that responded best to lines or edges at particular orientations, some requiring a specific position and others responding anywhere within a region, and cells grouped in columns by orientation and by which eye provided input. Their work showed that perception is built step by step, from simple features to more complex combinations.

Perception also depends on expectation and experience. People often fill in missing information, which is why Walter, before his diagnosis, sometimes thought he smelled coffee when his wife told him it was brewing: knowledge supplied what his weakened sense could not.

Smell Loss as an Early Sign

Doty (2012) reviewed research showing that loss of smell is one of the most common nonmotor features of Parkinson's disease, present in the large majority of patients, and that it often appears years before tremor or slowness. Disease-related changes appear early in the olfactory bulb and related regions, and smell testing can help distinguish Parkinson's disease from some conditions with similar movement symptoms. Smell loss alone does not mean someone will develop the disease, since it has many causes, but in combination with other signs it can support an early diagnosis.

Walter's history fits this pattern: his smell faded about six years before his tremor began.

Movement: From Plan to Action

Voluntary movement involves several systems. The primary motor cortex, in the frontal lobe, sends signals down the spinal cord to motor neurons that contract muscles, and areas in front of it help plan sequences. The cerebellum compares intended and actual movements, adjusting timing and coordination; damage there produces clumsy, poorly aimed movements. The basal ganglia, a group of structures deep in the forebrain, work in loops with the cortex to select which movements to make, start them and set their size and speed.

Walter's muscles are strong and his cerebellum intact; what fails is the circuit that tells a movement to begin and how big to be.

Dopamine and the Basal Ganglia

Kalia and Lang (2015) reviewed Parkinson's disease as a progressive disorder in which neurons in the substantia nigra that supply dopamine to the basal ganglia gradually die, along with the buildup of abnormal clumps of the protein alpha-synuclein. Much of this cell population is already gone before tremor or slowness first shows. The core motor features are slowness of movement, rigidity and resting tremor, often beginning on one side, and nonmotor features include smell loss, sleep disturbances, constipation, depression and later cognitive changes.

Walter's symptoms follow this picture. Without enough dopamine, the basal ganglia loops cannot properly release desired movements, producing slowness, short steps and small handwriting. Rigidity and reduced facial expression reflect the same problem in other muscle groups. His tremor began on one side, as it often does.

Treatment and What It Reveals

Levodopa, a precursor that the brain converts into dopamine, is the most effective treatment for motor symptoms. That it works confirms the central role of dopamine loss. It does not restore smell or stop the disease's progression, which shows that Parkinson's disease extends beyond the dopamine pathway. Over years, responses to levodopa can fluctuate and involuntary movements may appear.

For some patients, deep brain stimulation, in which electrodes deliver steady pulses to targets in the basal ganglia, reduces tremor and fluctuations. Its effects show that changing activity in these circuits can restore smoother movement even when dopamine cells are gone.

Living With the Disease

Exercise, including walking programs, cycling and balance training, helps maintain mobility, and speech therapy can address soft speech. Walter has joined a boxing-based exercise class for people with Parkinson's disease at a community center, which keeps him active and connected with others facing the same condition. His neurologist also screens for depression and sleep problems, which affect quality of life as much as tremor.

Conclusion

Walter's lost sense of smell and his slowing movements both trace to Parkinson's disease, affecting a sensory pathway early and a motor circuit later. Sensation converts energy into signals, perception builds them into experience step by step and movement depends on cortex, cerebellum and basal ganglia working together. Dopamine loss in the basal ganglia explains his motor symptoms, and treatment responses reveal how those circuits work.

References

Doty, R. L. (2012). Olfactory dysfunction in Parkinson disease. Nature Reviews Neurology, 8(6), 329-339. https://doi.org/10.1038/nrneurol.2012.80

Hubel, D. H., & Wiesel, T. N. (1962). Receptive fields, binocular interaction and functional architecture in the cat's visual cortex. The Journal of Physiology, 160(1), 106-154. https://doi.org/10.1113/jphysiol.1962.sp006837

Kalia, L. V., & Lang, A. E. (2015). Parkinson's disease. The Lancet, 386(9996), 896-912. https://doi.org/10.1016/S0140-6736(14)61393-3