Neural dynamics for a cognitive map in the macaque brain

The ability of the human brain to form a complex memory of an event experienced just a single time is astounding—and that memory can be stored and retrieved for decades. We sometimes casually refer to memory retrieval as “visualizing” the past—often with precise spatial and temporal detail intact. But how is such a mental map created in the brain? Research suggests that some of the brain regions responsible for forming and storing memory of past events, such as the hippocampus and the entorhinal cortex, are the same ones responsible for spatial navigation, implying a deep connection between the two processes.  However, how these processes are related, especially in primates, is largely unknown. Building on work in rodents showing that brain regions involved in memory are activated when the animals experience a virtual reality setting, in our experiments we will extend these results to primates. We will train monkeys to use a joystick to navigate virtual environments. Simultaneously, we will use several electronic brain implants that can measure the electrical activity of over a hundred neurons in the monkey’s hippocampus and entorhinal cortex. By analyzing this large set of neural data with sophisticated mathematical techniques, we can determine how these neurons represent the virtual environment. For example, it is known, in rodents, that certain neurons increase their activity when the animal traverses a particular, absolute point in virtual space. That is, the neuron will become excited when the animal visits the corner of the room, but not the middle. Other neurons will be active when the animal visits the middle of the room, but not the corner. In primate, how these neurons operate is less clear, but straightforward to study in a virtual reality environment. By working our the details of spatial navigation in primate memory brain regions, our work will lay the foundation for understanding how these mechanisms underlie the formation of complex memories, not only in monkeys, but in humans as well.