11 : -+Inhibition pt.2

Neuroscience of Executive Functions

Inhibition Overview

  • Inhibition is a crucial aspect of executive functions, allowing us to control impulses and focus on relevant tasks.

Prefrontal Cortex and Memory

  • Fuster and Alexander's key study:

    • Investigated prefrontal neuronal activity in delayed response tasks in monkeys.

    • Conclusion: Prefrontal neurons cannot store working memory information as they can't differentiate between memorized locations (Answer: C).

Sensory Recruitment Hypothesis

  • Definition: Increase in neuron firing during memory tasks to support sensory processing.

  • Key question: What finding does NOT support the hypothesis?

    • Correct answer: d (decoding from area IPS during delay period doesn't support it).

Summary of Executive Function Mechanisms

  • Basal Ganglia Circuitry

    • Direct and indirect pathways implicated in motor initiation and inhibition.

    • Rely on the right lateralized IFG–basal ganglia–STN circuit to control motor responses.

    • Controversy on extending the system to cognitive inhibition beyond motor control.

Inhibiting Distractors

  • Mechanism for focusing attention despite external distractions:

    • Top-down biasing signals regulate attention by altering neuron responses in V4 depending on stimulus effectiveness.

    • Effective stimulus enhances neuron response, whereas ineffective stimulus suppresses it.

Experiments on Inhibition

  • Face/House Paradigm: Explored how distractors impact neural activity.

    • Found that distractor categories exhibited decreased activity, providing evidence for inhibition.

  • TMS (Transcranial Magnetic Stimulation) was utilized to disrupt cortical functions and observe changes in distractor processing.

Top-Down Biasing Signal

  • Originates from frontally mediated signals that enhance target facilitation while inhibiting distractor influence.

  • Demands further research to isolate direct top-down inhibition effects from attention enhancements.

Dual-Task Paradigms

  • Important for understanding attention dynamics and updating action plans:

    • Psychological Refractory Period (PRP) hypothesis indicates a bottleneck in processing tasks when they are closely sequenced.

    • TMS influences both action updates and attentional detection, suggesting overlapping cognitive functions.

Role of rIFC (Right Inferior Frontal Cortex)

  • Important for stopping actions and detecting stimuli, perhaps serving dual roles in selecting overlapping action plans.

  • Subregions (rIFJ and rIFG) have distinct but related functions:

    • rIFJ is more involved in detecting attentional cues.

    • rIFG is crucial for updating action plans, not exclusive to stopping.

Theta Burst TMS

  • A non-invasive method used to induce neural suppression to examine cognitive functions:

    • cTBS inhibits, whereas iTBS enhances activity within targeted regions to perform cognitive tasks under controlled conditions.