Insights on ACC and Learning Volatility

May 23, 2025

Lecture Notes: Learning Volatility and the Anterior Cingulate Cortex

Introduction

  • Presenter: Tim Behrens from Oxford
  • Topic: Learning volatility and the Anterior Cingulate Cortex (ACC)
  • Background: Tim Behrens is recognized for contributions in neuroimaging, particularly fiber tracking and models of decision-making and evaluation.

Key Concepts

  • ACC Significance: Important structure in the brain, particularly in neuroscience.
  • Focus: Learning from outcomes to improve future decision-making.

Experimental Results

Result 1: Reinforcement Guided Decision-Making

  • Study: Effect of ACC lesions in macaque monkeys.
  • Findings: Without ACC, monkeys relied only on the most recent trial for decision-making.
  • Integration Curve: Normally, monkeys integrate multiple past experiences to decide effectively.

Result 2: Social Decision-Making and Evaluation

  • Study: Monkeys' social behaviors and decision-making.
  • Findings: Monkeys will sacrifice food to view higher-status monkeys.
  • Lesions Effect: Lesions in the ACC's gyral portion altered social decision-making, decreasing interest in social stimuli.

Understanding the Anterior Cingulate Cortex

  • Roles: Influences decision-making and social valuation.
  • Connections:
    • Sulcus: Linked to motor output and action-awareness regions.
    • Gyrus: Connected to emotional and social information regions.
  • Commonality: Both regions process reward and motivation information.

Computational Explanation

  • Objective: Explain differences in learning and decision-making using computational models and fMRI data.
  • Integration Length: Varies based on environment; faster learning in volatile environments.

Experiment with Humans

  • Task: Choosing between blue and green squares with varying reward probabilities.
  • Learning: Humans adjust learning rates based on environment volatility, similar to optimal Bayesian learners.

Reinforcement Learning Theory

  • Concepts:
    • Prediction Error: Difference between expected and actual outcomes.
    • Learning Rate: Determines the weight of new information versus past information.
  • Application: Adaptive learning in humans and animals.

fMRI Studies

  • Decision-making Activation: Broad brain activation during decisions.
  • Outcome Monitoring: Specific activation in the ACC during outcomes, influenced by environmental volatility.
  • Key Findings:
    • Activity in ACC correlates with volatility and learning rates.
    • The anterior cingulate sulcus is crucial during outcome evaluation.

Social Valuation Experiment

  • Setup: Subjects receive advice from a confederate and evaluate its trustworthiness.
  • Learning Problems:
    • Probability of reward (action-outcome learning).
    • Probability of confederate's reliability (social evaluation).
  • Results: Social and reward information processed similarly, engaging reinforcement learning.

Conclusions

  • ACC Role: Crucial in learning and integrating information for decision-making.
  • Dissociation Yet Similarity: Gyrus processes social info; sulcus processes action info, both share computational roles.
  • Inter-individual Variability: Differences in ACC activation correspond to learning speed and style among individuals.

Q&A Highlights

  • Monkeys likely share some anatomical features related to social evaluation with humans.
  • Fast learners may not necessarily be fast meta-learners due to experiment complexity.
  • Humans may over-interpret patterns in random sequences, indicating a different cognitive process.
  • Social biases and collaboration were examined, showing initial biases can influence learning.

Closing Remarks

  • The lecture emphasized the importance of computational models in understanding brain functions, particularly in social valuation and decision-making processes.
  • Thanks to key contributors and a note on the applicability of findings across species.

Full transcript