Lecture 16 Frontal Lobes

Frontal Lobes and Executive Function

Goals

  • Explore the anatomy of the frontal lobes, particularly the prefrontal cortex (PFC).
  • Understand the impact of frontal lobe damage on behavior and executive processes.
  • Examine syndromes associated with frontal lobe lesions.
  • Discuss the role of the prefrontal cortex in working memory and attentional control.

Anatomy of the Frontal Lobes

The frontal lobes constitute approximately 41% of the cerebral cortex, making them the largest brain lobe. They are critical for higher-order cognitive functions and include:

Key Regions

  1. Primary Motor Cortex (Precentral Gyrus):
    • Executes motor commands.
  2. Premotor Cortex:
    • Coordinates motor planning.
  3. Prefrontal Cortex (PFC):
    • Divided into:
      • Dorsolateral PFC (dlPFC): Executive function and working memory.
      • Ventrolateral PFC (vlPFC): Rule following and inhibition.
      • Ventromedial PFC (vmPFC): Emotional regulation and motivation.
      • Orbitofrontal Cortex: Decision-making and social behavior.

Thalamic Connections

  • The PFC is defined by its reciprocal connections with the mediodorsal thalamus, facilitating communication with other cortical and subcortical areas.

Frontal Syndromes

Dysexecutive Syndrome

Case study of Patient W.R.: – Background: – Presented as alert, intelligent, and well-dressed with no apparent deficits in basic cognition. – History of social and professional success. – Symptoms: – Severe planning deficits (e.g., did not take the bar exam after law school). – Apathy and anhedonia (e.g., lost interest in tennis and social life). – Inappropriate affect (e.g., indifference to his mother’s death and grim medical prognosis). – Neurological Findings: – A large bilateral astrocytoma (“butterfly glioma”) in the frontal lobes. – Impaired working memory, planning, and motivation.

Disinhibition Syndrome

  • Characterized by inappropriate and impulsive behaviors driven by environmental stimuli.
  • Examples from Lhermitte’s studies:
    • Patients acted on objects inappropriately (e.g., undressing in a doctor’s home, injecting with a syringe left out).
  • Utilization Behavior:
    • The inability to suppress automatic responses to objects in the environment.

Orbital Frontal Syndrome

  • Symptoms include impulsivity, poor decision-making, and lack of social judgment.
  • Often associated with acquired psychopathy, as seen in cases of ventromedial and orbital frontal lesions.

Prefrontal Cortex and Executive Function

Rule Maintenance and Shifting

  • Oddball Tasks:
    • Used to study rule shifting and attention. Requires a response to infrequent stimuli while ignoring others.
    • Activation of the dlPFC increases during task-switching and rule changes.
  • Wisconsin Card Sorting Task (WCST):
    • Measures the ability to shift between categorization rules.
    • Frontal lobe patients often perseverate, failing to adapt to new rules.

Planning and Problem Solving

  • Tower of London Task:
    • Requires strategic planning to achieve a goal in minimal moves.
    • Patients with left anterior frontal lesions perform poorly on this task.
  • Matchstick Problem:
    • Tests creative problem-solving and breaking conventional rules.
    • Frontal patients sometimes outperform controls on novel solutions due to reduced rule adherence.

Frontal Lobes and Working Memory

Functions of the dlPFC

  • Maintenance:
    • Holding information temporarily for immediate use.
  • Manipulation:
    • Reorganizing information within working memory (e.g., mentally solving arithmetic).
  • Attention:
    • Sustained focus on internal representations or tasks.

Tasks and Findings

  • Oculomotor Delayed Response Task:
    • dlPFC lesions impair the ability to maintain spatial locations during delays.
  • High Filtering Tasks:
    • Generating multiple responses (e.g., uses for a rope) activates the dlPFC.
    • Frontal patients struggle with such tasks, often producing fewer options.

Prefrontal Control of Attention

  • The PFC interacts with the thalamus to regulate attention.
  • Thalamic Reticular Nucleus (TRN):
    • Acts as a mediator for sensory input gating under prefrontal control.
  • Event-Related Potential Studies:
    • Show PFC modulation of sensory systems via thalamic circuits.

Emotional Regulation and Counterfactual Thinking

Reappraisal and Emotional Regulation

  • Reappraisal involves reframing negative situations to reduce emotional impact.
  • Processes:
    • Keeping initial appraisals in working memory.
    • Inhibiting emotional responses.
    • Generating and maintaining alternative interpretations.
  • Frontal Lesions:
    • Impair the ability to generate counterfactuals and reappraise situations, leading to rigid, concrete thinking.

Key Terms

  • Dysexecutive Syndrome: Deficits in planning, working memory, and motivation.
  • Disinhibition Syndrome: Inability to suppress inappropriate actions.
  • Perseveration: Repetition of a behavior despite changing rules or contexts.
  • Wisconsin Card Sorting Task (WCST): A neuropsychological test of rule shifting and executive function.
  • Thalamic Reticular Nucleus (TRN): Modulates sensory input under prefrontal control.

This lecture integrated case studies, neuroanatomy, and experimental findings to explore the diverse roles of the frontal lobes in cognition, behavior, and emotional regulation. Future lectures will delve into the neural basis of memory and decision-making.

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