**1. Hippocampal memory functions**

After report of a patient H.M. [1], the various areas of research, including psychology, neuroscience, cognitive science, and behavioral science, have researched the hippocampal function for learning and memory. The patient H.M. suffered epileptic seizures as a child. He receives a resection of a portion of temporal lobe including hippocampus for treating the seizures when he was 27 years old. Although the treatment reduced the symptom of seizure without lack of

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

some his cognitive and memory functions, such as intelligence quotient (IQ), conversational ability, perceptual capability, working memory, semantic memory formed before surgery, and procedure memory, the patient H.M. had minor symptoms of retrograde amnesia and severs anterograde amnesia [1]. Thus, Scoville and Milner [1] suggested that the hippocampus is necessary for the encoding of episode memory but not retrieval and storage of the memory. After then, for understanding the hippocampal function in detail, animal researchers have examined what kind of learning task is necessary for being solved by hippocampal functions. In the electrophysiology study, O'Keefe and Nadel [2] showed that the rodents' hippocampal CA1 neuron was activated by the memory of placement. They named "place cell" as hippocampal CA1 neuron which associated information of placement and suggested the cognitive theory that hippocampus was important for solving spatial learning by using eight arms radical maze and Morris water maze. In the hippocampal lesion study, Bouffard and Jarrard [3] compared hippocampal lesion rat and control rat without hippocampal lesion on eight arms radical maze. For solving this task, rats need to learn the arms that were choose once time by using peripheral environmental cue outside of the maze. The performance of the rats with hippocampal lesion was less than that control rats. Also, it has examined on the Morris water maze. For solving the task, the rats need to understand own position and goal position from some environmental stimuli outside the maze and reach the goal position by cueing these stimuli. The rats with hippocampal lesion increase a latency that reached an invisible goal platform as compared with control rats on the maze [4]. In addition, several research studies showed the universal function that hippocampus plays role in a spatial learning over other species, such as fishes [5], birds [6, 7], and primate [8, 9], suggesting that the cognitive map theory is one of the popular hippocampal function theories having adaptive possibility for various species. On the other hand, some researchers have reported that hippocampal function was important for solving a certain type of nonspatial stimulus discrimination task.

### **2. Negative patterning task**

Configural association theory suggests that the hippocampus plays role in learning the relationship between multiple sensory stimuli [10]. According to the theory, animals have two systems, elemental and configural association systems, for processing sensory information, and they adapt successfully to various situations in the external world by using them. The elemental association system forms representation of single stimulus, such as the single stimulus associated with reinforcement or punishment. However, in the external world, a compound stimulus combining multiple stimuli may sometimes have a significant meaning. The configural association system forms one of the configural representations by associating between multiple stimuli when some of them are presented simultaneously or serially. Sutherland and Rudy [10] proposed that hippocampal function was necessary for the formation of configural representations for compound stimuli. After then, the theory was revised by some researchers [11–13] and latest theory that the hippocampus is important for configural presentation for compound stimulus in exclusive-or (XOR) tasks such as negative patterning task and positive patterning task. In the negative patterning task, rats are reinforced for operant responses when either one of two different sensory single stimuli, such as tone (T) or light (L), is presented (T+ or L+). In contrast, rats are not reinforced when both stimuli are presented (TL−). In this task, compound stimulus had overlapping element with single stimuli. For solving this task, rats need to, thus, form the configural representation for compound stimulus and discriminate between compound stimulus and single stimuli.

Gray and McNaughton [14] proposed the conflict resolution model for the hippocampal function and behavioral inhibition. The model suggests that the hippocampal function plays role in the resolution of conflict between incompatible goals or response tendencies. According to this model, the hippocampal function modulates the weight of negative information and, specifically, increases it, thereby inducing behavioral inhibition [14, 15]. Interestingly, this theory may also explain why the hippocampus is important for solving the compound stimulus in the negative patterning task. In the negative patterning task, either one of stimuli A and B is presented alone when they signal a "go" response, but the stimuli are presented simultaneously when they signal a "no-go" response. Thus, the compound stimulus had incompatible goals or response tendencies. Animals need to increase the weight of negative information and inhibit operant response for compound stimulus. Both the conflict resolution model and the configural association theory suggest a role of the hippocampus in solving the negative patterning task.
