Week 7 The Cerebrum

Objectives

  • Introduction to functional areas of the cerebrum.
  • Recognize and identify the most common Brodmann's Areas.
  • Recognize and label functional areas of each lobe.
  • Apply knowledge to understand anticipated function after brain injury.
  • Define the following disorders and name a lesion location for each of the disorders:
    • Agnosia
    • Astereognosis
    • Visual agnosia
    • Auditory agnosia
    • Optic ataxia
    • Apraxia
    • Motor perseveration
  • Understand how damage and dysfunction in certain areas can affect occupational performance.

Cerebrum: The Basics

Functions of the Cerebrum

  • Perception
  • Moving voluntarily
  • Using language and nonverbal communication
  • Understanding spatial relationships
  • Using visual information
  • Making decisions
  • Consciousness
  • Emotions, mind-body interactions
  • Remembering

Diencephalon

Components of the Diencephalon

  • Thalamus
    • Regulates flow of information to the cortex.
  • Hypothalamus
    • Integrates behaviors with visceral functions.
    • Associated with the pituitary gland.
  • Epithalamus
    • Includes pineal gland.
  • Subthalamus
    • Part of basal ganglia circuit.

Basal Ganglia

Functions of the Basal Ganglia

  • Vital for normal motor function.
    • Sequence movements
    • Regulate muscle tone and muscle force
    • Select and inhibit specific movements
  • Involved with cognitive functions, behaviors, and emotions.

Subcortical White Matter

Three Categories

  • Projection fibers
    • Example: Internal capsule
  • Commissural fibers
    • Example: Corpus callosum
  • Association fibers
    • Connect areas within the same hemisphere.

Cerebral Cortex

Structure of the Cerebral Cortex

  • Collection of cell bodies, axons, and dendrites.
    • Granule- interneurons
    • Pyramidal- output
  • Contains layers that are differentiated by size and connectivity.

Localized Functions

Specific Cortical Functions

  • Primary sensory cortex
    • Discriminates sensory information.
  • Primary motor cortex
    • Provides descending control of motor output.
  • Secondary sensory cortex
    • Engaged in complex analysis of sensation.
  • Motor planning areas
    • Organize movements.
  • Association cortex
    • Controls behavior, interprets sensation, and processes emotions and memories.

Primary Somatosensory Cortex

Perception

  • The interpretation of sensation into meaningful forms.
  • Involves interaction of brain, body, and environment, including memory, motivation, and expectations.

Secondary Sensory Areas

Areas and Functions

  • Somatosensory (Areas 5, 7)
    • Function: Stereognosis and memory of the tactile and spatial environment.
    • Lesion: Asterognosis.
  • Visual (Areas 18-21)
    • Function: Analysis of motion, color; recognition of visual objects; understanding of visual spatial relationships; control of visual fixation.
    • Lesion: Optic ataxia or visual agnosia.
  • Auditory (Areas 22, 42)
    • Function: Classification of sounds.
    • Lesion: Auditory agnosia.

Use of Visual Information: Action and Perceptual Streams

  • Dorsal stream: Involved in processing the object's spatial location relative to the viewer and guiding movements.
  • Ventral stream: Concerned with object recognition; this stream helps identify what the object is.

Primary Motor Cortex

Cortical Motor Planning Areas

  • Located anterior to the primary motor cortex:
    1. Supplementary motor area (SMA)
    • Involved in the initiation of movement, orientation of the eyes and head, and planning bimanual and sequential movements.
    1. Premotor cortex
    • Learns goal-oriented actions and prepares, selects, and initiates movements.
    1. Inferior frontal gyrus
    • Includes Broca’s area (usually in the left hemisphere).
    • Involved in planning movements of the mouth during speech.
    • Processes emotional, social, and spatial information (right hemisphere).

Clinical Application

Terminology

  • Motor Perseveration
    • Uncontrolled repetition of a movement.
  • The Four A’s
    • Aphasia: Inability to understand or express language.
    • Apraxia: Inability to execute skilled movement and gestures.
    • A form of Motor Agnosia.
    • Includes Constructional Apraxia.
    • Agnosia: Inability to recognize objects.
    • Astereognosis: Inability to recognize objects by touch.

Thalamic Lesions

Effects of Thalamic Lesions

  • Can compromise or eliminate contralateral sensation.
  • Proprioception is most affected.
  • Rare thalamic pain syndrome may occur.
  • Intralaminar nuclei: Associated with consciousness.
  • Lateropulsion (Pusher syndrome): Related to lesions in the posterior thalamus.

Pituitary Tumors

Characteristics of Pituitary Tumors

  • Usually benign and slow-growing.
  • Symptoms can result from:
    • Mass pushing on surrounding structures.
    • Hormonal hyposecretion or hypersecretion.
  • Common symptoms include:
    • Headaches
    • Nausea
    • Vomiting
    • Irregular menses and lactation
    • Sexual dysfunction
    • Bitemporal hemianopia.

Internal Capsule Lesions

Impact of Internal Capsule Lesions

  • Occlusion or hemorrhage of arteries supplying the internal capsule is common.
  • Even small lesions may have severe consequences.

Callosotomy

Purpose of Callosotomy

  • Surgical procedure performed in cases of intractable epilepsy.
  • Aims to prevent excessive firing from spreading between hemispheres.
  • Can lead to symptoms such as 'alien hand syndrome.'
  • Specialized exams include assessments of vision and stereognosis:
    • Right visual field/hand corresponds to the left hemisphere (language).
    • Left visual field/hand corresponds to the right hemisphere (spatial).

Primary Sensory Area: Loss of Discriminative Sensory Information

Lesions Affecting Secondary Sensory Areas: Agnosia

Primary Motor and Premotor Cortex Lesions

Effects of Lesions

  • Can result in dysarthria, noted by spasticity or paresis of muscles used in speaking.
  • Tan also causes contralateral paresis and loss of selective motor control.
    • Damage particularly affects the fine movements of the hand and face.
  • Lesions in the premotor cortex affect:
    • Speed and automaticity of contralateral reaching and grasping.
    • Sequential movements on the contralateral side.
    • Gait and posture.

Inferior Frontal Gyrus Lesions

  • Can lead to Broca’s aphasia, characterized by difficulty expressing oneself using language or symbols.
  • Most commonly associated with the left hemisphere.

Functional Neurologic Disorders (FND)

Characteristics

  • Symptoms unexplained by other classical neurological or medical conditions.
  • Not based on malingering or faking.
  • Diagnosis relies on incompatibility between physical exam results and function.

Functional Sensory Disorders

  • Symptoms may include dizziness, somatosensory, or visual disturbances.

Functional Movement Disorders

  • Symptoms may include weakness, abnormal movements, tremors, dystonia, and gait disorders.

Signs and Symptoms of Stroke

Effects of Stroke

  • Depend on the location and size of the lesion.
  • Acute neurological deficits affecting more than 25% of survivors of brain infarctions include:
    • Hemiparesis
    • Ataxia
    • Hemianopia
    • Visual-perceptual deficits
    • Aphasia
    • Dysarthria
    • Sensory deficits
    • Memory deficits
    • Problems with bladder control.

Tumors

Overview of Tumors

  • Spontaneous abnormal growth of tissue forming a mass.
  • Symptoms include mild to moderate headaches, nausea, and vomiting.
  • Tumors arising in the brain are named based on the type of cell involved.
  • Prognosis depends on:
    • Histology
    • Size and location of the tumor
    • Age of the patient
    • Effectiveness of surgical, chemical, and radiation therapy.

Epilepsy

Characteristics of Epilepsy

  • Defined by sudden attacks of excessive cortical neuronal discharge leading to interference with brain function.
  • Focal seizures affect only a restricted area of the cortex.
  • Generalized seizures affect the entire cortex.
  • Following a seizure, a person may experience postictal confusion and lack of memory of the event.
  • Common treatments include drug therapy, brain surgery, behavioral adjustments, and vagus nerve stimulation.