<P> Based on Papez's experiment with aggression in rats and other studies, it was initially believed that the circuit was involved with emotion . The circuit connects the hypothalamus and the cortex and acts as the emotional system of the brain . "The cingulate cortex projects to the hippocampus, and the hippocampus projects to the hypothalamus by way of the bundle of axons called the fornix . Hypothalamic effects reach the cortex via a relay in the anterior thalamic nuclei ." </P> <P> However, there has not been additional proof of the circuit's role in emotion over the years . Now, the Amygdala is thought to play a key role in emotion, a structure that was not a part of the Papez circuit until 1952 when MacLean included it in the modified version of the circuit, the limbic system . </P> <P> In the past few years, many experiments have been done that involve structures of the Papez circuit . Moreover, many cases where structures of the Papez circuit have been damaged show changes that indicate its real function . </P> <P> Theta waves are used to measure activity in mainly the hippocampus but can be used to measure other brain regions as well . Strong synchronization of theta waves in the hippocampus and anterior ventral thalamus has been observed . Although theta waves between the hippocampus and the anterior dorsal and anterior medial regions in the thalamus showed no synchronization, scientists have seen a marked increase in firing rates of the neurons in the brain regions . Overall, based on theta wave experimentation, some components of the Papez circuit have shown to indeed have a connection and work together . Also, theta waves are thought to be linked to learning and memory . Consequently, many scientists believe that the Papez circuit is involved with memory because of theta wave experiments . Some scientists have narrowed it down to specifically spatial and episodic memory . </P>

Which of the following structures is a component of the papez circuit