PROJECT SUMMARY
Our decisions are influenced by recent experiences (i.e., history dependence). The control of
history dependence relies on the posterior parietal cortex (PPC). However, PPC also serves
many other functions such as working memory and sensorimotor control. This proposal aims to
elucidate how PPC circuits perform multiple functions, a critical step towards identifying the
causes and treatments of specific PPC malfunctions. We hypothesize that different functions
involve different subcircuits in PPC, each with distinct input-output connectivity. We will test this
hypothesis, focusing on the function of history dependence and two projection targets of PPC,
the dorsal striatum (STR) and posterior secondary motor cortex (pM2). Although both targets
have been implicated for history-dependent decisions, our preliminary results indicate that the
PPC neurons projecting to each target are largely distinct, suggesting that the two pathways
may have distinct functions. Here we propose to take three parallel approaches to uncover
which of the two pathways mediates history dependence and to characterize long-range inputs
to each pathway. First, we will compare the history bias information encoded by PPC neurons
projecting to STR or pM2, using a combination of two-photon calcium imaging and retrograde
labeling in mice exhibiting history-dependent decision bias. Second, we will determine the
necessity of PPC-STR and PPC-pM2 pathways for history-dependent decisions, by
optogenetically inactivating each pathway and assessing its effect on history-dependent bias.
Lastly, we will map long-range inputs specific to the two pathways that contribute to the
formation of history-dependent bias in PPC, using retrograde trans-synaptic rabies tracing.
Together, the results will reveal whether PPC contains a subcircuit dedicated to history
dependence and what constitutes the input and output pathways of that subcircuit. Answers to
these questions will lay the solid groundwork for future research that delineates the inter-areal
circuits underlying decision-making and other PPC functions. Furthermore, the identification of
function-specific pathways may point to neural substrates for targeted intervention with less risk
of compromising other functions.