The most characteristic nature of consciousness is its introspective function. How does it become possible to objectify ‘the self’ without a mirror? The operation to disconnect corpus callosum or frontal commissure which connects both the right and left hemispheres had been done mostly in the 1960’s to cure epileptic patients (9). The purpose of the operation is to stop the spreading of abnormal electric discharge over the whole brain. In the process of that research, extremely interesting facts other than functional asymmetries between right and left hemispheres were found. The cerebrum in which the corpus callosum is disconnected by the operation is called split-brain. After the operation, split-brain epileptic patients show no special extraordinariness and can live like normal people. They can ordinarily do behavior, speech and recognition. However, when investigated in detail, peculiar facts were revealed (10-12). Here, let us take the following matters into consideration: Each hemisphere mostly governs the motor events of the opposite side of the body, most people have the language area in the left hemisphere, and split-brain patients have disconnected corpus callosum but have intact optic chiasm. Moreover, optic nerves from the right half retina of the right eye connect to the right hemisphere without passing through optic chiasm, and those from the left half retina of the right eye connect to the left hemisphere passing through optic chiasm. Similarly, optic nerves from the right half retina of the left eye connect to the right hemisphere passing through optic chiasm, and those from the left half retina of the left eye connect to the left hemisphere without passing through optic chiasm. On the other hand, since the retina is curved, the right half retina of each eye sees the left half of a visual field and the left half retina of each eye sees the right half of it (12). Accordingly, when the subject gaze at the central fixation point of a translucent screen set at a proper distance before his eyes, visual information of the left side of the fixation point can be transmitted to only the right hemisphere, and those of the right side of it can be transmitted to only the left hemisphere. In case of normal people, since intact corpus callosum is provided, visual information are held in common by both hemispheres due to exchange of visual information between both hemispheres. On the other hand, in case of split-brain patient with disconnected corpus callosum, since exchange of visual information between the right and left hemispheres are not executed, visual information from left half of visual field can be transmitted to only the right hemisphere and those from right half of it can be transmitted to only the left hemisphere. For example, if the split-brain subject is asked what an object he saw when the letter, ‘tea’, at the left side and the letter, ‘cup’, at the right side of the fixation point were reflected on the screen from behind by tachistscope, he who has language area in the left hemisphere answered verbally that he saw the letter, ‘cup’. However, surprisingly, when he is directed to select an object which he saw by his left hand, he selects the card on which the letter, ‘tea’ is written. Similarly, shown a picture of some object such as a pear at the left side of the fixation point and required to select an object on the table using blind touch, he can do it with the left hand but not with the right hand. Moreover, when required to answer verbally, he cannot say what object he selected. On the contrary, when shown a picture of a pear at the right side of the fixation point, the subject can select a pear using blind touch with the right hand but cannot with the left hand. In this case, he can say an object verbally to be a pear. Like this, a split-brain patient shows the peculiar and surprising behavior, but more surprising fact is that he has no feelings of the strangeness of his own behavior. If he has (introspective) consciousness, will he not think “why did I behave like this?”? It is summarized that these experimental results are observed in common regardless of the subject’s sex and nationality and so on, nevertheless with some variations and exceptions. On these results, the former scientists demonstrated two views: 1) the right and left hemispheres have two separate consciousness which are integrated into one by the corpus callosum (10-12). 2) the right and left hemispheres have two separate consciousness regardless of corpus callosum disconnection (13-15). However, these results should be comprehended as evidence showing that (introspective characteristic of) consciousness is lost by corpus callosum disconnection. The right and left hemispheres have not two separate consciousness though each hemisphere is able to judge and recognize independently (it is not confirmed that each hemisphere alone shows the introspective characteristic of consciousness), both hemispheres form consciousness only when they are connected by the corpus callosum. Here, let us turn our attention to mirror neurons.