Whereas brain studies of symbol manipulations, including thinking and tool-use, have been extensively performed in human with brain-imaging techniques, neuronal data for this issue have been limited. However, recent studies with monkeys have provided some interesting data that allow us to hypothesize neuronal mechanisms of symbol manipulations. For example, neuronal groups of the prefrontal cortex code and retain behavioral meaning/abstract information for guiding goal-directed motor acts. These neurons appear to play a role in manipulating and retaining of symbolic information. Further, the prefrontal cortex is well known as a center of working memory, which contains “executive” associated with manipulation of information and control of brain systems. Based on these and other findings, we can hypothesize that the prefrontal cortex has a neuronal system for “executive symbol manipulation”. The executive is a central neuronal system of goal-directed symbol manipulations for controlling other brain systems, and this system would first evolve for tool-use and eventually develop for language and other symbol manipulations. Since the executive symbol manipulation is a possible neuronal system of the prefrontal cortex and can be examined with non-human primates, this hypothesis would be useful for leading neuronal studies of brain mechanisms of symbol manipulations.

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When using a tool it becomes an extension of the hand both physically and perceptually—the tool is incorporated into our body image, or body schemata. We have shown in monkeys that, visual receptive fields of bimodal (tactile and visual) neurons were altered to include the entire length of the rake to represent neural correlates for assimilation of the tool into our own body-image. Also, we showed the evidence that these neurons can also code the body-image projected onto the video monitor, perhaps corresponding to its “iconic” representation. When above described representations were further advanced, it would become totally free from physical constraints of the actual world to become a (pre-) symbolic one to represent evolutionary precursors of higher cognitive functions such as using tools, and eventually leads to evolution of human language or to metaphysical thoughts.

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I summarized our recent studies, which assessed chimpanzees' symbolic representation of sequence. Chimpanzees have demonstrated their capacities to integrate fractal information about pairs of stimuli into an ordered series by showing transitive inference. Language is not a necessary prerequisite for using transitive inference. But the concept of number may promote understanding of ordered sequence. A chimpanzee trained in ordinality demonstrated a perfect transitivity. Transitivity is frequently used for the assessment of implicit ordinal number comprehension in human infant. Symbolic distance effects were obtained in a numerical ordering task by the chimpanzee, named Ai, which suggests that the chimpanzee perform the task by making reference to a linear representation of number order. Also in this task, the chimpanzee first explore the number space, calculating the ordinal relationships and spatial locations of each number, and then used this stored information to guide her subsequent responses. These strategies were highly similar to that of expected to be used by humans but not by macaque monkeys.

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Although many cases have been reported on impairment of tool use and behavioral disturbance due to brain damage, the precise brain mechanisms regulating human behavior are still unknown.
In this report, an outline of behavioral abnormalities caused by brain damage, including utilization behavior (UB), imitation behavior (IB), and apraxia are presented. Next, a case of UB and IB elicited only by a key person is reported, and interpretation of his symptoms is discussed. Lastly, the general structure of information processing in the human brain for tool use and behavior are discussed. I speculate that there are two distinct systems in the human brain, that is, a control system and a substantial information processing system. The former corresponds to attention and emotion. This distinction should have importance when considering tool use and behavior in human beings.
A right-handed, 70 year-old man suffered bilateral anterior cerebral artery occlusion that resulted in bilateral frontal lobe infarction. He was inert, and his attention was impaired. He showed typical UB and IB which were elicited only by his chief physician and only in examination situations. Both UB and IB were lacking in his daily life and were never elicited by his family members or other medical personnel. Another report also gives evidence of cases in which a key person is required for UB and/or IB to be elicited.
Generally, an object could be considered to always show its meaning as a tool, which implies that its affordace emerges from the object itself. The behavior presented by the key person also can be regarded as a releaser for the patient to imitate behavior. Thus his essential impairment can be attributed to failure to grasp the correct relation of the meaning of objects or of behaviors and situations. This should be called a type of semantic impairments.
On the other hand, the patient's inertia and impaired attention is indicative of emotional disturbance. In fact, his cerebral lesions involve some parts of the limbic system. This suggests that he lost active perception which resulted in his being very easily captured by external stimuli. His unique symptoms should not be attributed to the traditional explanation in which UB and/or IB emerge from simple disinhibition of the parietal lobe function from the frontal lobe function.

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The acceleration phenomenon of infant word acquisition can not be explained by simple neural learning mechanism of brain. To explain it, we have to assume some prior knowledge or structure in brain that is specific for language. However, the assumption is not plausible from evolutional view. It is natural to assume that the mechanism also exist in animal brain and is used for different purpose originally, and it is re-used for language in evolutional process. To examine possibility of the idea, we apply memory model PATON for the simulation of infant primary word acquisition process, and propose a model of its acceleration process. From the result, we discuss on how language is specific for human by examining the back grounding brain mechanism that enable the rapid word acquisition.

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The aim of this paper is to present the structure and classification of past sequences, e.g., flashbacks, with reference to actual scenes from movies and televised movies, with a new technique for transcription. An analysis of the techniques used in the scenes revealed the following points: (1) close-ups and voice-overs are used to indicate “who remembers,” (2) reshowing the prior scenes or references to the past are used to indicate “when the event occurred,” and (3) changing the color or brightness of the screen is used to indicate “breaks” between the present and the past. The analysis reveals that many techniques, or cognitive artifacts, are employed to depict past sequences, which often result in redundancy. The notion of cognitive artifacts is discussed further, particularly with respect to their systematic aspects.

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The Modern Japanese suffix oki has two meanings. The interpretation of oki is affected mainly by four factors, among which are the unit and the amount expressed by the word to which oki is attached. This paper proposes a hypothesis on mental scanning (Scanning Hypothesis), which gives us a unified explanation of these two influencing factors. Scanning Hypothesis posits that the scanning procedure consists of four processes (i.e. element observation, reference adjustment, simple attribution and relational attribution), and that the order of these scanning-constituting processes is reversed according to whether the object is homogenious or heterogenious. When the object is homogenious, the order is as follows: element observation, reference adjustment, simple attribution, relational attribution. When the object is heterogenious, the order of performance is element observation, relational attribution, simple attribution, and referece adjustment. Furthermore, it will be shown that this hypothesis is also effective in explaining several other linguistic phenomena.

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