The cerebral cortex, basal ganglia, thalamus, and cerebellum work together to control our thoughts and actions. These brain regions process sensory information, coordinate movements, and enable complex cognitive functions like decision-making and language.

Lateralization refers to how the left and right brain hemispheres specialize in different tasks. While the left side handles language and logic, the right side excels at spatial skills and emotions. The corpus callosum allows the hemispheres to communicate and collaborate.

Cerebral Cortex: Lobes and Functions

Lobes and their associated functions

• The cerebral cortex is divided into four main lobes: frontal, parietal, temporal, and occipital
  • Each lobe is associated with specific functions and processing of sensory, motor, and cognitive information
• The frontal lobe is involved in executive functions, such as planning, decision-making, and impulse control, as well as motor control and language production (Broca's area)
• The parietal lobe processes sensory information related to touch, pressure, temperature, and proprioception
  • Plays a role in spatial processing and navigation
• The temporal lobe is involved in auditory processing, language comprehension (Wernicke's area), and memory formation, particularly in the hippocampus and related structures
• The occipital lobe is primarily responsible for visual processing, including color, shape, and motion perception

Association areas and their roles

• Association areas, such as the prefrontal cortex and the posterior parietal cortex, integrate information from multiple sensory modalities
  • Contribute to higher-order cognitive functions, like attention, working memory, and problem-solving
• The prefrontal cortex is involved in complex cognitive processes, such as decision-making, planning, and social behavior
• The posterior parietal cortex integrates somatosensory, visual, and auditory information to create a unified representation of space and guide goal-directed actions

Basal Ganglia and Thalamus: Organization and Functions

Basal ganglia: components and their roles in motor control

• The basal ganglia are a group of subcortical nuclei that play a crucial role in motor control, learning, and execution of complex motor patterns
  • The main components of the basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus
• The basal ganglia receive input from the cerebral cortex and send output back to the cortex via the thalamus, forming a feedback loop that modulates motor behavior and learning
• The direct and indirect pathways within the basal ganglia have opposing effects on motor output
  • The direct pathway facilitates movement
  • The indirect pathway inhibits movement
• Dysfunction of the basal ganglia can lead to movement disorders
  • Parkinson's disease is characterized by tremor, rigidity, and bradykinesia
  • Huntington's disease is characterized by uncontrolled, jerky movements called chorea

Thalamus: a relay station for sensory and motor information

• The thalamus is a relay station that processes and integrates sensory and motor information before sending it to the cerebral cortex
  • Consists of multiple nuclei, each with specific functions and connections to different cortical areas
• Plays a role in regulating sleep-wake cycles, attention, and consciousness
• Damage to the thalamus can result in sensory deficits, memory impairments, and changes in arousal and awareness
  • Thalamic lesions can cause sensory loss (anesthesia), abnormal sensations (paresthesia), or pain (thalamic pain syndrome)
  • Thalamic strokes can lead to anterograde amnesia, difficulty forming new memories

Cerebellum: Motor Control and Coordination

Cerebellum's role in motor control and learning

• The cerebellum is a hindbrain structure that plays a critical role in motor control, coordination, balance, and learning of motor skills
• Receives input from the vestibular system, proprioceptors, and the cerebral cortex, and sends output to the motor cortex and brainstem motor nuclei
• Compares intended movements with actual movements and makes fine adjustments to ensure smooth, accurate, and coordinated motion
• Involved in the learning and automation of motor skills through a process called long-term depression (LTD), which weakens synaptic connections between parallel fibers and Purkinje cells

Consequences of cerebellar damage

• Damage to the cerebellum can result in various motor deficits
  • Ataxia: impaired coordination and balance
  • Dysmetria: inaccurate targeting of movements
  • Dysdiadochokinesia: difficulty performing rapid alternating movements
• Cerebellar lesions can also cause gait disturbances (wide-based, staggering gait), speech difficulties (slurred or scanning speech), and impaired eye movements (nystagmus)

Lateralization: Left vs Right Hemispheres

Functional specialization of the cerebral hemispheres

• Lateralization refers to the functional specialization of the left and right cerebral hemispheres for certain cognitive and behavioral processes
• The left hemisphere is typically dominant for language processing (both production and comprehension), sequential processing, and analytical thinking
  • Lesions in the left hemisphere often result in language disorders (aphasia) and difficulties with mathematical reasoning
• The right hemisphere is more involved in visuospatial processing, facial recognition, emotional processing, and holistic thinking
  • Right hemisphere damage can lead to neglect syndromes, impaired spatial awareness, and difficulty recognizing emotions in others

Interhemispheric communication and split-brain studies

• Lateralization is not absolute, and both hemispheres contribute to most cognitive functions to some degree, often working together in a complementary manner
• The corpus callosum, a large bundle of nerve fibers, connects the two hemispheres and allows for communication and integration of information between them
• Studies of split-brain patients, whose corpus callosum has been surgically severed to treat severe epilepsy, have provided insights into the specialized functions of each hemisphere and the role of interhemispheric communication in cognition and behavior
  • In these patients, information presented to one hemisphere cannot be directly accessed by the other, leading to interesting dissociations in behavior and perception
  • For example, a split-brain patient may be able to name an object presented to the left visual field (right hemisphere) but unable to verbally describe it, as the language centers are typically in the left hemisphere