Amygdala-prefrontal cortex interactions in the primate brain and the neural basis of credit assignment

Thesis

An important adaption for life in changeable environments, such as those occupied by many primate species, is the ability to learn the contingencies that prevail between events and their consequences. Credit assignment consists in the capacity to correctly associate the value of an outcome to the event or choice that led to it. Interactions between amygdala and prefrontal cortex have been suggested to support credit assignment. Chapter 1 reviews the anatomy and function of areas supporting value-guided learning and decision making that may contribute to credit assignment mechanisms. This chapter also reviews a group of methodological approaches that have been used or are currently being optimized to investigate these mechanisms. Chapter 2 focuses on the reconstruction of the anatomical pathways supporting value-guided computations and that may provide the scaffolding for credit assignment to take place. Both macaque monkeys and humans are investigated using the same methodological approach which additionally makes possible direct comparison of anatomical and connectional features in the two species. Chapter 3 demonstrates the potential of an offline focused transcranial ultrasound stimulation protocol applied at low-intensity to reversibly and minimally-invasively modulate the activity coupling of subcortical and deep cortical areas like the amygdala and anterior cingulate cortex of the primate brain without the necessity for surgical intervention. Chapter 4 exploits these properties of focused transcranial ultrasound stimulation to investigate the behavioural deficits in credit assignment caused by the disruption of activity in the primate lateral orbitofrontal cortex. The behavioural results reported in this chapter suggest that ultrasound stimulation targeted to this area impairs the capacity to correctly assign credit to a previous choice, specifically following positive feedback, thereby disrupting the impact that the integrated history of choice option-outcome contingencies has on future behaviour. Chapter 5 highlights the neural basis of credit assignment and the consequence of interfering with activity in lateral orbitofrontal cortex. After stimulation, brain activity encoding the choice-option outcome contingencies through credit assignment was disrupted but the response to reward only was not. Chapter 6 reviews the results reported throughout the thesis aiming to connect them together in a similar framework and discuss them with reference to the current scientific literature on amygdala-prefrontal cortex connectivity and credit assignment.

Authors: Folloni, D

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: amygdala; orbitofrontal cortex; decision-making; MRI; ultrasound; connectivity; learning; brain stimulation
• Subjects: Neuroscience