<P> The intermediate hippocampus has overlapping characteristics with both the ventral and dorsal hippocampus . Using anterograde tracing methods, Cenquizca and Swanson (2007) located the moderate projections to two primary olfactory cortical areas and prelimbic areas of the medial prefrontal cortex . This region has the smallest number of place cells . The ventral hippocampus functions in fear conditioning and affective processes . Anagnostaras et al. (2002) showed that alterations to the ventral hippocampus reduced the amount of information sent to the amygdala by the dorsal and ventral hippocampus, consequently altering fear conditioning in rats . Historically, the earliest widely held hypothesis was that the hippocampus is involved in olfaction . This idea was cast into doubt by a series of anatomical studies that did not find any direct projections to the hippocampus from the olfactory bulb . However, later work did confirm that the olfactory bulb does project into the ventral part of the lateral entorhinal cortex, and field CA1 in the ventral hippocampus sends axons to the main olfactory bulb, the anterior olfactory nucleus, and to the primary olfactory cortex . There continues to be some interest in hippocampal olfactory responses, in particular, the role of the hippocampus in memory for odors, but few specialists today believe that olfaction is its primary function . </P> <P> Over the years, three main ideas of hippocampal function have dominated the literature: response inhibition, episodic memory, and spatial cognition . The behavioral inhibition theory (caricatured by John O'Keefe and Lynn Nadel as "slam on the brakes!") was very popular up to the 1960s . It derived much of its justification from two observations: first, that animals with hippocampal damage tend to be hyperactive; second, that animals with hippocampal damage often have difficulty learning to inhibit responses that they have previously been taught, especially if the response requires remaining quiet as in a passive avoidance test . Jeffrey Gray developed this line of thought into a full - fledged theory of the role of the hippocampus in anxiety . The inhibition theory is currently the least popular of the three . </P> <P> The second major line of thought relates the hippocampus to memory . Although it had historical precursors, this idea derived its main impetus from a famous report by William Beecher Scoville and Brenda Milner describing the results of surgical destruction of the hippocampi (in an attempt to relieve epileptic seizures), in Henry Molaison, known until his death in 2008 as "Patient H.M." The unexpected outcome of the surgery was severe anterograde and partial retrograde amnesia; Molaison was unable to form new episodic memories after his surgery and could not remember any events that occurred just before his surgery, but he did retain memories of events that occurred many years earlier extending back into his childhood . This case attracted such widespread professional interest that Molaison became the most intensively studied subject in medical history . In the ensuing years, other patients with similar levels of hippocampal damage and amnesia (caused by accident or disease) have also been studied, and thousands of experiments have studied the physiology of activity - driven changes in synaptic connections in the hippocampus . There is now universal agreement that the hippocampi play some sort of important role in memory; however, the precise nature of this role remains widely debated . </P> <P> The third important theory of hippocampal function relates the hippocampus to space . The spatial theory was originally championed by O'Keefe and Nadel, who were influenced by E.C. Tolman's theories about "cognitive maps" in humans and animals . O'Keefe and his student Dostrovsky in 1971 discovered neurons in the rat hippocampus that appeared to them to show activity related to the rat's location within its environment . Despite skepticism from other investigators, O'Keefe and his co-workers, especially Lynn Nadel, continued to investigate this question, in a line of work that eventually led to their very influential 1978 book The Hippocampus as a Cognitive Map . There is now almost universal agreement that hippocampal function plays an important role in spatial coding, but the details are widely debated . </P>

Cerebellum is to memory as hippocampus is to