PhD defence I.M. (Ivo) Silva Marcelo

Dissertation in short:

The work presented in this thesis characterizes different levels at which experience-based representations emerge in neural systems, and how these support and inform individuals to operate and adapt to widely diverse challenges throughout their life span. We first describe how cued fear memories are encoded in sparse networks of neurons in the Lateral Amygdala, by physiological changes in their neural properties, namely heightened intrinsic neural excitability and potentiation of glutamatergic inputs. For these acquired fear memories to inform future behavior and environmental adaptation, it is crucial that their neural representations persist through time. For this purpose, we characterize how contextual fear memories are maintained long-term, through memory consolidation mechanisms. Specifically, we identified fear memory-specific transcriptional changes in sparse networks of neurons in the Dentate Gyrus region of the Hippocampus, that are fundamentally required for memory consolidation and its maintenance over time. Equally important to learning what to fear, is to correctly decide how to behave given different environmental circumstances or options. One approach for making such decisions is to have a “mental model of the world”, and choose according to predicted consequences arising from selected behaviors. In this line, we show, in a sequential decision task, that neural populations in the Anterior Cingulate Cortex (ACC) not only represent a complete model of the task environment, but also provide predictions of future environmental states given chosen task actions, identical to model-based decisions. Extending from decision-making, perhaps the most complex, and equally crucial, behavioral adaptations an individual needs to undertake pertains to its social environment. For this purpose, we describe the role of ACC neural representations in competitive social interactions. We demonstrate that the ACC predicts and encodes distinct social states within individual brains, both preceding and during competitive interactions. Importantly, joint representations of social competition across brains of interacting individuals allows for enhanced prediction of social outcomes, validating a putative new level of experience-based representations, beyond individual nervous systems.