Sensorimotor System Overview

Sensorimotor System

• The sensorimotor system controls motor output, flowing from higher to lower levels, processing sensorimotor programs with real-time feedback.
• Higher levels (e.g., association cortex) plan and design movements.
• Lower levels (e.g., spinal motor circuits) execute the movement.
• Parallel processing is done by the basal ganglia and cerebellum to manage timing and sequence.
• Association cortex ("chop the onion") plans initial movement, secondary motor cortex refines the movement design, and primary motor cortex executes the specific motor sequence.
• Brainstem motor nuclei and spinal motor circuits are involved in the final execution of the movement.

Brain Changes with Movement Practice

• Movement sequences are grouped as units instead of individual parts (response chunking).
• Learning complex skills (e.g., typing) involves memorizing words, rather than individual letters.
• Shifting control to lower levels frees up higher-level cognitive functions.
• Motor equivalence means multiple ways to perform the same task.

Posterior Parietal Association Cortex (PPC)

• Integrates information about body position and external objects.
• Damage leads to contralateral neglect (e.g., neglecting the left side of space), deficits in language (left hemisphere damage) or apraxia(issues with movement).
• Damage in PPC causes issues with initiating movements, not weakness or coordination issues.

Dorsolateral Prefrontal Association Cortex (DPFC)

• Involved in executive functions: evaluation, problem-solving, working memory, learning.
• Damage leads to impaired decision-making, problem-solving, and working memory.

Mirror Neurons

• Activated during both performing and observing a motor action.
• Related to empathy and understanding others.
• Located in ventral premotor cortex and inferior parietal lobule.

Primary Motor Cortex (M1)

• Organization of different body parts in a specific order.
• Damage causes deficits in moving specific body parts independently.
• Other impairments include reduced speed, accuracy, and strength of movement and asterognosis (identification of objects by touch).

Cerebellum

• Receives input from primary and secondary motor cortex, brainstem nuclei, and somatosensory and vestibular systems.
• Compares planned movements with actual movements.
• Ensures precise timing, sequence, and control of movement (e.g., coordination and balance).
• Problems with this area can cause deficits in timing and controlling movement.

Basal Ganglia

• Parallel processing of timing and sequencing with the cerebellum.
• Involved in initiating movements.
• In Parkinson's disease, there is reduced "Go" and increased "Stop" due to reduced substantia nigra neurons.
• In Huntington's disease, symptoms include excessive movement.

Dopamine Pathways

• Involved in both "go" and "stop" pathways in the basal ganglia and thalamus.
• Dopamine is involved in both the initiation and control of movements.

Parkinson's Disease

• Marked by reduced "Go" and increased "Stop" due to substantia nigra neuron loss.
• Symptoms include stiffness, resting tremor, slow movement, mask-like face, pain, and depression.
• Treatment includes L-DOPA (to increase dopamine) and deep brain stimulation.

Huntington's Disease

• Affects neurons, particularly in the striatum; symptoms include excessive movement.
• Rare and highly genetically determined disorder.

Sensory Feedback

• Sensory systems monitor body's response and feed that response back to the brain to adjust movements.
• Reflexes are automatic responses and do not rely on feedback to adjust movements.
• Exceptions for sensory feedback are ballistic movements (sudden, brief movements).

Clinical Depression

• Five or more symptoms for at least two weeks (one major symptom is from 1-2)
• Symptoms include depressed mood, loss of interest, weight changes, sleep disturbances, fatigue decrease in energy, feelings of worthlessness, thoughts or ideas of death.

Hypomania

• Persistent mild elevation of mood
• Increased energy, activity, social interaction, thoughts, and goal pursuing behaviour.

Mania

• Distinct period of elevated mood, energy, and activity.
• At least one week of elevated mood with additional symptoms
• Can be described by: inflated self-esteem, decreased need for sleep, more talkative, racing thoughts, distractibility, increase in goal-directed activity, and potential for consequential actions.

Bipolar 1 and Bipolar 2

• Both involve mood swings, but Bipolar I also includes manic episodes.
• Bipolar II is characterized by hypomanic episodes and periods of depression.

Neuroplasticity

• Changes in nervous system resulting from experience.
• It involves formation of new neural connections throughout life.
• Three mechanisms of neuroplasticity are described as functional plasticity, structural plasticity, and neurogenesis.
• Critical periods during development allow for high plasticity.

Neurogenesis

• Formation of new neurons in the brain.
• Primarily occurs during development, but also exists in the adult brain.

Visual System as a Model of Neuroplasticity

• Children with cataracts (阻碍视觉) experience reorganization of the brain's visual system.
• The brain prioritizes the functional non-deprived eye.
• Changes are different in adults than children.

Motor Equivalence

• Multiple ways to perform the same action.
• This ability is achieved through brain reorganization and is essential for adaptation.

Treatment of Parkinson Disease

• L-DOPA is used as a treatment
• Medication (to increase dopamine) and deep brain stimulation.

Aging

• Brain volume decreases gradually after age 40, more rapidly after 70.
• Specific brain areas like the frontal cortex shrink faster compared to other areas.
• Neurotransmitters such as dopamine and serotonin decline with age.
• Accumulation of white matter damage.
• There is a small degree of Alzheimer's pathology and small neuronal loss.
• Socioemotional changes may occur (e.g., smaller social group, more emotionally close partners).

Ethical Considerations (Including Brain Computer Interfaces)

• Brain computer interfaces need to address ethical issues, like safety, decision control, harm prevention, and user capacity, informed consent, and privacy.
• Biases, culpability and potential harm to one's identity that can be caused by the technology need to be examined.

Distinguishing Between Clinical Conditions

• There are distinct symptom presentations, criteria, and etiologies for different neuropsychological conditions (MCI, AD, Bipolar disorders, etc.).
• Differentiating conditions can require medical history, clinical testing, observation of symptoms (including memory performance, behaviour, daily living activities) and brain imaging.

Artificial Intelligence

• Big data has five key characteristics: Volume (amount of data), Variety (formats/types), Velocity (speed of data), Veracity (accuracy), and Value (usefulness derived from the data).
• Artificial intelligence is capable of processing brain-health data that includes structured and unstructured data.
• Machine learning is a subset of AI systems that can categorize and predict using specific algorithms.

Cognitive Rehabilitation Therapy

• Cognitive Rehabilitation Therapy Aims to improve cognitive functioning through compensation, plasticity, and recovery.
• Examples of applications include TBI and stroke.
• Strategies used in therapy can include mnemonic strategies, external supports, and targeting neglected areas.

BCI (Brain Computer Interface)

• Defines BCI: artificial interface for the brain to interact with the external world using different mechanisms (speech, typing, movement).
• Types of BCI include non-invasive (e.g., EEG), semi-invasive (e.g., electrodes), and invasive.
• Applications include controlling movement, communication, etc.