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A 48-year-old woman presented with a 2-week history of headache. The headache was so severe in the standing position that she could hardly stand up. The results of general and neurological examination were unremarkable. MRI studies of the brain showed diffuse pachymeningeal gadolinium enhancement on the T(1) weighted images. The cerebrospinal fluid (CSF) opening pressure on lumbar puncture was 70 mm H(2)O. MR myelography and RI-cisternography disclosed leak of cerebrospinal fluid at the lumbar level. Then, we diagnosed her as headache associated with liquorrhea. Two weeks later, she noticed an inability to recognize familiar faces, including her own face in the mirror. The Cambridge Face Memory Test (CFMT) proved prospagnosia. Brain MRI revealed multiple subdural hematomas below the bilateral fusiform gyrus. SPECT demonstrated diffuse hypoperfusion in the brain including bilateral fusiform gyrus. Months later, she showed gradual improvement of prospagnosia. Follow-up brain MRI revealed disappearance of both subdural hematomas and diffuse pachymeningeal gadolinium enhancement. SPECT demonstrated marked improvement of cerebral blood flow in the whole brain including the right temporal-occipital lesion. This is the first report of acquired prospagnosia during the course of liquorrhea causing subdural hematomas. Subdural hematoma below a right fusiform gyrus may cause reversible prospagnosia.

A 66-year-old, right-handed male, was admitted to our hospital with difficulty in recognizing faces and colors. He had suffered a stroke in the right occipital region three years earlier that had induced left homonymous hemianopsia, but not prosopagnosia. A neurological examination revealed prosopagnosia, color agnosia, constructional apraxia, and topographical disorientation, but not either hemineglect or dressing apraxia. The patient was unable to distinguish faces of familiar persons such as his family and friends, as well as those of unfamiliar persons such as doctors and nurses. Brain MRI demonstrated an old infarction in the right medial occipital lobe and a new hemorrhagic infarction in the left medial occipital lobe, including the fusiform and lingual gyrus. It is unclear whether a purely right medial occipital lesion can be responsible for prosopagnosia, or whether bilateral medial occipital lesions are necessary for this occurrence. The current case indicated that bilateral medial occipital lesions play an important role in inducing porsopagnosia.

A 58-year-old man with metastatic brain tumor in his right occipito-temporal region was operated, using craniectomy. He had no neurological symptoms preoperatively. The tumor was 2.5 cm in diameter with minor perifocal edema. Two days after total removal of the tumor, typical prosopagnosia appeared, in which he could not recognize his wife's face as well as faces of medical stuff. He could see them as a whole, and described them undistinguishably from each other. He used voices, movements and clothing to recognize a familiar person. His recognition and semantic knowledge of people were found to be intact and he could recognize certain parts of the face (e.g. the nose or the mouth). He could clearly see other parts of the body, the environment and other objects, in color. The prosopagnostic condition lasted for a few weeks and slowly disappeared. Prosopagnosia caused by surgical procedure has been rarely reported. Although postoperative prosopagnosia is likely to be transient, it should be recognized as a complication in occipito-temporal cortex.

We review recent researches in neural mechanisms of facial recognition in the light of three aspects: facial discrimination and identification, recognition of facial expressions, and face perception in itself. First, it has been demonstrated that the fusiform gyrus has a main role of facial discrimination and identification. However, whether the FFA (fusiform face area) is really a special area for facial processing or not is controversial; some researchers insist that the FFA is related to 'becoming an expert' for some kinds of visual objects, including faces. Neural mechanisms of prosopagnosia would be deeply concerned to this issue. Second, the amygdala seems to be very concerned to recognition of facial expressions, especially fear. The amygdala, connected with the superior temporal sulcus and the orbitofrontal cortex, appears to operate the cortical function. The amygdala and the superior temporal sulcus are related to gaze recognition, which explains why a patient with bilateral amygdala damage could not recognize only a fear expression; the information from eyes is necessary for fear recognition. Finally, even a newborn infant can recognize a face as a face, which is congruent with the innate hypothesis of facial recognition. Some researchers speculate that the neural basis of such face perception is the subcortical network, comprised of the amygdala, the superior colliculus, and the pulvinar. This network would relate to covert recognition that prosopagnosic patients have.

We review recent researches in neural mechanisms of facial recognition in the light of three aspects: facial discrimination and identification, recognition of facial expressions, and face perception in itself. First, it has been demonstrated that the fusiform gyrus has a main role of facial discrimination and identification. However, whether the FFA (fusiform face area) is really a special area for facial processing or not is controversial; some researchers insist that the FFA is related to 'becoming an expert' for some kinds of visual objects, including faces. Neural mechanisms of prosopagnosia would be deeply concerned to this issue. Second, the amygdala seems to be very concerned to recognition of facial expressions, especially fear. The amygdala, connected with the superior temporal sulcus and the orbitofrontal cortex, appears to operate the cortical function. The amygdala and the superior temporal sulcus are related to gaze recognition, which explains why a patient with bilateral amygdala damage could not recognize only a fear expression; the information from eyes is necessary for fear recognition. Finally, even a newborn infant can recognize a face as a face, which is congruent with the innate hypothesis of facial recognition. Some researchers speculate that the neural basis of such face perception is the subcortical network, comprised of the amygdala, the superior colliculus, and the pulvinar. This network would relate to covert recognition that prosopagnosic patients have.

We reported a patient who showed agnosia for streets and homes unaccompanied by prosopagnosia of familiar faces following infarction in the right occipital lobe. A 70-years-old right-handed man admitted to our department because of sudden development of visual impairment. He had left hemianopsia, left unilateral spatial neglect and slight visual memory disturbance but no other neurological abnormalities. His verbal memory was maintained intact. He was, however, unable to distinguish the sceneries of buildings and streets regardless of their familiarities and often got lost in the hospital. His topographical abilities in map-sketching and route-description were partially impaired depending upon the familiarity of targets; the disability was observed toward unfamiliar targets. His ability in facial recognition was also partially impaired depending upon the familiarity of persons. The patient was unable to distinguish faces of unfamiliar persons, such as nurses and doctors whom he met following stroke, whereas he was able to distinguish faces of familiar persons, such as his family and friends. The brain MRI demonstrated infarction in the right medial occipital lobe including parahippocampal gyrus, lingual gyrus and fusiform gyrus. In general, the manifestation of agnosia for streets and houses is associated with prosopagnosia. The present case, however, exhibited only the former in association with the partial manifestation of the latter. The fact suggests that those two are independent syndromes. The present case also showed a dissociation in the abilities of topographical and facial recognition according to the familiarity of targets. The process for the retrieval and reference of acquired information and that for the acquirement of new visual information may work in an independent manner.