2.4 Parietal Lobe

Chapter 5: The Parietal Lobes

Overview of Parietal Lobes

• The parietal lobes are involved in the perception of somatosensory events and spatial functions.

• Damage to this area results in a wide array of symptoms.

• The parietal lobe can be divided into two sections:

  • Anterior Region (Postcentral Gyrus): Responsible for somatosensory perception, tactile perception, and body sense.

  • Posterior Region: Associated with language, spatial orientation, neglect, symbolic synthesis, apraxias, cross-modal matching, and memory.

Page 1: Structure of the Parietal Lobes

• The parietal lobes have arbitrary boundaries with some subdivisions of little functional significance.

• Key Features:

  • The anterior area noted as the sensory strip is posterior to the Rolandic fissure.

  • The sensory area may not have precise localization.

• The complexity of symptoms post-lesion can be attributed to various interconnected functions of this lobe.

Page 2: Somatosensory Perception

Sensory Strip Representation

• The post-Rolandic sensory strip displays a point-to-point localization:

  • Areas with high sensory acuity (e.g., fingertips) have more cortex dedicated to them.

  • Cortical representation is mainly contralateral; two sensory systems operate:

    • Lemniscal: Touch sensation.

    • Extralemniscal: Temperature and pain.

Two-Point Threshold Test

• The sensitivity of skin regions can be assessed using two sharp points to measure the smallest discernible distance in sensation.

Page 3: Impacts of Lesions

Effects of Primary and Secondary Cortex Lesions

• Lesions can alter sensation from the body, causing:

  • Anesthesia or dysesthesia (loss/alteration of sensation).

  • Kinesthetic information disruption, affecting spatial perception and limb positioning.

• Disagreements exist regarding sensory representation asymmetry in left vs. right hemispheres based on various studies.

Page 4: Tactile Perception and Body Sense

Somatosensory Agnosias

• Tactile deficits are termed somatosensory agnosias, categorized as:

  • Astereognosis: Inability to recognize objects by touch alone.

  • Asymbolia: Equivalent to astereognosis.

• Assessment can be conducted using tasks like the Seguin-Goddard Formboard.

Types of Asomatognosia

• Anosognosia: Lack of awareness of body limb positions and possible sensory loss, often seen with right-sided lesions.

• Autotopagnosia: Inability to localize or name body parts, often resulting from left-side injuries.

• Finger Agnosia: Specific difficulty with the identification and naming of fingers, assessed through various tests.

Page 5: Complex Relationships in Cognitive Deficits

• Astereognosis can overlap with visual object agnosia, suggesting interlinked cognitive processes.

• Common tests for visual agnosia include:

  • Gollin Figures

  • Mooney Closure Faces Test

  • Unconventional Views of Objects Test

Page 6: Spatial Orientation and Impairments

Understanding Spatial Representation

• Spatial orientation relates directly to functions associated with visuospatial agnosia, where challenges arise in:

  • Identifying object orientations relative to the observer.

• Tests include:

  • Pool Reflections Test: Identifying patterns in reflection.

  • Stick Test: Reproducing spatial configurations presented by the examiner.

Memory and Spatial Trials

• Assessments like the Tactual Performance Test and Benton Visual Retention Test help identify spatial memory deficits.

Page 7: Disturbances of Spatial Location

• Patients can have issues following familiar routes, affecting personal navigation.

• Assessment includes performing tasks like following a map (Locomotor Map Following Task), revealing parietal lesion impacts.

Page 8: Right-Parietal Lesions

• Right parietal lesions are associated with more pronounced difficulties in spatial location and left-right discrimination.

• Tests include the Money Road Map Test to evaluate navigational skills.

Page 9: Spatial Neglect

Nature of Spatial Neglect

• Spatial neglect leads to a lack of attention to one side of space, commonly impacting the opposite side of the lesion.

• Right lesions typically result in left-sided neglect.

• Symptoms observed include:

  • Bumping into objects on the neglected side.

  • Neglecting one half of written tasks or meals.

Attention vs. Awareness

• Studies have indicated that patients can process neglected information at an unconscious level, leading to preference for intact stimuli when given choices.

Page 10: Treatment Strategies

• Treatments involve enhancing attention to neglected spaces or using contralateral limb activation.

• Imagining movement may prove useful for reducing neglect.

• Spontaneous remission and phases of recovery are noted, evolving from allesthesia to simultaneous extinction.

Page 11: Symptoms and Neural Connections

Concept of Neglect

• Attention, sensory perception, and spatial awareness are linked factors behind neglect.

• Clinical observations highlight how patients may display misdirected responses, indicating errors in spatial perception.

Page 12: Cognitive Interaction in Neglect

• Tasks assessing drawing abilities reflect parietal lobe functionality, including drawing errors unique to lesion impacts.

• Observations reveal differences in errors based on the location of a lesion.

Page 13: Inter-sensory Association

Cross-modal Integration Deficits

• Posterior parietal lesions affect tactile-visual integration.

• The left hemisphere emphasizes identity and semantics, while the right handles location and visuospatial properties, contributing to higher-level deficits.

Page 14: Short-term Memory and Parietal Lesions

• Some parietal lesions can lead to issues with short-term auditory memory (e.g., rapid forgetting in patients like KF).

Page 15: Gerstmann Syndrome

Overview

• Gerstmann syndrome combines agraphia, acalculia, right-left confusion, and finger agnosia, though it's debated as a unitary syndrome.

Page 16: Language Function

• Posterior parietal areas contribute significantly to language functions alongside the frontal and temporal lobes, particularly in auditory reception and reading.

Page 17: Conclusion

Summary of Parietal Functions

• Parietal lobe lesions lead to diverse functions impacted, with variabilities due to patient-specific cognitive strategies.

• The bilateral representation of functions complicates understanding, revealing an interplay between spatial and verbal processes in cognitive tasks.