The limbic system, located in the medial wall of the cerebrum, is involved in recognition, emotion, and memory formation. Especially, the amygdala and hippocampal formation, which lie under the medial temporal cortices, receive the sensory information of all modalities from the sensory association cortices, and integrate this higher order information into emotion and memory. Thus, the amygdala and hippocampal formation are essential in the higher order brain functions as key structures for emotion and memory systems in the brain, respectively. In this article, we review recent studies in neuroanatomy, neuropsychology, and behavioral sciences regarding the limbic system. Based on these studies, 1) neural circuits in the limbic system including the amygdala and hippocampal formation, 2) neural mechanisms of emotion and memory, and 3) interaction between emotion and memory systems are discussed.

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    Recently Haxby et al. (2000) have proposed a model of distributed neural system for face perception which emphasizes a distinction between the processing system for invariant and changeable aspects of faces. Invariant aspects of faces are important for the recognition of individuals whereas changeable aspects of faces such as eye gaze and emotional expression facilitate social communication. In this article we focus on the latter aspect and describe recent psychological studies which have examined the interaction between emotional facial expression and face/gaze direction. The experimental research revealed that (1) automatic attentional shift by gaze-cueing was modulated by emotional facial expression and that (2) the perceptual processing of emotional facial expression and of face/gaze direction interacts, facilitating the detection of the negative faces when the gazes are directed toward the observer. Overall, the evidence provided by psychological research is quite consistent with that from the neuroscientific research. This presents a convincing demonstration that both approaches can be most fruitful when taken in concert.

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    Face neurons processing specifically faces have been found in the inferotemporal cortex. These neurons detected the distances between eyes and mouth or between two eyes. This suggests that there might be face specific area in the human brain. Faces convey complex information such as species, individual identity, and emotional state. Information analysis of responses of single neurons to faces has revealed that global information (human, monkey or geometrical shapes) was represented from the start of the responses and fine information (identity, expressions) was represented 50ms after the peak of global information.

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    The brain has at least two roles as an organ : One is to put a person in an adequate environment, the other is to communicate verbally.
    1) Face of Street (town)
    A scenary such as street is an important environmental stimulus and its recognition indicates a lot to the recognition-behavior of man. Identifying the face of street is necessary in order to put the self in an adequate environment. The patient of this kind tends to consider his house as not his own and thinks the familiar street as strange. This phenomenon is similar to the prosopagnosia. Thus the agnosia for scene consists of the impossibility to recognize the face of street. Common MRI lesion in our 6 cases lies in the right parahippocampal gyrus.
    2) Face of Person (human-being)
    Human face is also an important enviromental stimulus. Identifying human face precisely is very important in putting one in an adequate environment and in pursuing a social life. The failure to recognize the human face is called prosopagnosia. The lesion lies in the right fusiform and lingual gyri just posterior to the one which causes the scien agnosia.
    The pathophysiology for both the scien agnosia and the prosopagnosia seams to be the disturbance in the right occipito-temporal lobe-hippocampus system. Thus the system of the postero-inferior part of the right hemisphere and hippocampus plays a major role in the recognition of the street and person.
    3) Recognition of facial expression
    The disturbance of recognition of facial expression doesn't occur in most of the patients suffering from prosopagnosia. The lesions which reveal the disturbance of recognition of facial expression include the basal ganglia and amygdala. Facial expression is one of the ways to communicate non-verbally and its recognition is another role of the brain.
    People use the different brain structure in identifying the human face from in understanding the facial expression.

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    Specificity of face recognition was discussed in terms of prosopagnosia and Williams syndrome researches. First, we examined prosopagnosic patients on a new face recognition test with superimposed computed images by morphing. The results showed that prosopagnosic patients had wide differential threshold suggesting the low accuracy of judgment compared with normal subjects ; but more important findings were that patients tended to choice the more similar comparative stimuli on the similarity judging task as well as normal subjects. These findings reflect categorical perception and they suggest that the disturbed categorical level of recognition for prosopagnosia may be defined by expertise level. Recently some fMRI studies gave evidence in support of our findings and cast some doubt on specificity of face recognition. Second, I took up some recent reports concerning face recognition for Williams syndrome patients. Williams syndrome is known as a genetically based disorder with cognitive characteristics expressed as “peaks and valleys” ; they show relative strengths in language and facial processing and profound impairment in spatial cognition, which supports modularity of face recognition. But some reports investigated local/global cognitive ability respectively on both face and non-face recognition, which concluded that Williams syndrome patients recognized faces in terms of local features instead of global features unlike normal subjects. They also constrain the specificity of face recognition. In conclusion, we have many problems to be solved to declare that a face is special.

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    We reported a case of pure agraphia of Kanji due to left temporal tumor. K. S. is a right-handed 75-year-old male. On 8th February, 1999, he suddenly experienced writing difficulty with Kanji but not Kana or Katakana. His reading ability for both Kanji and Kana was normal. MRI revealed left temporal tumor which occupied mainly Wernicke's area with perifocal edema. SPECT with ECD revealed widespread low blood flow in the left temporal lobe. Inability of Kanji writing was drastic and persisted during anti-edema therapy with steroids. The patient was able to copy presented Kanji quickly and correctly at a glance of the given target. Although he also showed mild Wernicke aphasia, common conversation was almost intact.
    Recently many authors have reported specific agraphia of Kanji due to left posteroinferior temporal damage. But most cases showed agraphia and alexia of Kanji initially, and later only agraphia of Kanji remained. In the case of K. S., however, agraphia of Kanji appeared suddenly.
    Usually each Kanji has several pronunciations, and any given pronunciation corresponds to several Kanji. That is, Kanji and pronunciations form correspondences of many to many. Kana form correspondences of one to one, with some exceptions. To write Kanji words correctly, semantic control is believed to be necessary. We postulated that both Kana and Kanji are controlled by semantics, pronunciation and letter form. Kana writing is thought to be mainly controlled by pronunciation and Kanji writing equally controlled by all three factors.
    To date, “visual images” of letters are thought to be stored in the left angular gyrus, and many reports of agraphia have been based on this assumption. But the concept of “visual images” of letters is very ambiguous. Here we propose a new writing and reading system for Kanji and Kana which emphasizes the concept of “control” to the frontal motor area. In addition we postulate that “visual images” of letters do not exist in the left angular gyrus.

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    We compared the discourse performance of 15 patients with early stage Alzheimer's disease (AD), 15 matched controls (NC), and 15 patients with mild to highly-moderately severe aphasia (AP). A single-frame picture description task and a procedural discourse task were used to elicit discourse. The stimulus picture was created to enable the subjects to produce inferential statements. In order to develop a new analytical system that could delineate clinical profiles of discourse in patients with AD, our analysis of discourse focused on qualitative characteristics, i. E. responsiveness, understanding task requirements, coping strategies for the task, and drifting away from the task, as well as information content. The content of information included the following : the people's behavior, climate, inferred information, and topic of the picture for the picture description task, and the explanation in an organized fashion of the steps necessary in a procedure for the procedural task. All of the participants were able to respond to the task instructions. Significant differences were revealed between the AD and NC groups for the majority of the items in the analysis. Some of the patients with AD exhibited difficulties in understanding the task requirements, poor coping strategies, and drifting away from the task. They also obtained lower scores on people's behavior, climate, picture topic, and explanation of the necessary steps of a procedure in an organized fashion. The AP group differed significantly from the AD group with respect to the understanding of the task requirements and people's behavior, coping strategy, and drifting away from the task. We were able to delineate the characteristics of discourse in patients with AD who are in the early stages, using the new discourse analysis system. The results are discussed in relation to the qualitative differences in discourse among the subject groups.

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