**3. Hippocampal lesion and negative patterning task**

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

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

stimulus discrimination task.

12 Electroencephalography

**2. Negative patterning task**

Several previous studies reported that hippocampal lesions impair the negative patterning task performance [10, 16–18]. However, some studies have reported no effects of hippocampal lesions on the negative patterning task [19]. Davidson et al. [19] reported abnormal behavioral inhibition of the operant response after hippocampal lesions, suggesting a lack of learning ability for compound stimuli. Moreover, hippocampal lesions result in an abnormal operant response, such as response persistence [20]. Therefore, in order to build a more solid foundation for the configural association theory and conflict resolution model, the relationship between hippocampal activity and the negative patterning task needs to be investigated by means other than hippocampal lesions.
