Henry: I agree with Kathy, because how could anything happen to the part that, like, just isn't in the light?

-FOURTH-GRADE DISCUSSION ON WHAT HAPPENED TO BLUEPRINT PAPER EXPOSED TO

LIGHT (AAAS LESSON)

''Well. God made all these things; so how come we have to worry about them?''

THIRD-GRADER

INTRODUCTION

Ordinarily the human nervous system completes its maturation in fourteen to sixteen years, provided it receives sufficient amounts of the correct kinds of stimuli. While there is little evidence that an environment rich in all kinds of relevant stimuli can substantially speed up the maturation process. there exists a great deal of evidence that, deprived of appropriate stimulation, maturation can he prevented from proceeding normally or even be permanently arrested. The body acts as though its development runs according to a kind of biological clock that has been set for things to happen in sequence at certain intervals. But the clock needs winding. Environmental stimulation seems to supply that need. If through accident or parental dereliction an infant born with a normal set of eyes is kept in the dark for the first seven years or so of its life, the probability that it will develop normal vision on exposure to light is small. Each year that light fails to reach the eyes, the chances of normal development become smaller. There exist, in other words, periods of time in the course of maturation when sufficient amounts of appropriate stimuli must be present in order for the potential of a system to be realized. Deprived of the appropriate stimuli, the new connections will not form. Even though the organ systems may still be present in a basic form -e.g., rods and cones in the retina still remain-the system is no longer biochemically capable of interacting with light stimuli. Consequently, the potential of the system cannot be realized. If a child is deprived of speech in early years, his cognitive development may be permanently blocked. Children, for example, need to he exposed to a great deal of human speech and verbal interaction with adults or older normally developed peers in the period of life from two months until seven or eight years of age if their cognitive development is to proceed normally. Adults have a remarkable capacity to perceive patterns in the sounds children make and to feed back to them corrected versions of the patterns. Thus the properties of speech are learned almost as a gestalt, and a network of mental connections is built simultaneously. Deaf children who fail to receive some kind of equivalent speech training early enough in their development often never recover from an early' language deficit. The apparatus for speech or speech-equivalent communication may be there, but it must be stimulated if it is to develop normally.

This chapter is meant to give the reader some understanding of those biological aspects of learning and thinking which seem to be especially relevant to the modes of inquiry which modern elementary science programs advocate.

It will show how the blend of emotion with intellect through the mediating effect of a section of the brain called the reticular formation probably occurs. Like a cake that can fall flat when the ingredients are not properly blended, so successful mental functioning depends on achieving optimal mixes of signals from different parts of the brain. If emotions run at too low or at too high a level, the cake will fall- the learner fails to get involved with the problem, or he gets so excited or so anxious that he cannot function. Somewhere in between the extremes lies the proper blend of mind and emotion to drive the investigative spirit on.

There is a central coordinator in the nervous system called the reticular formation (see Figure 7-1), which lies in the brain stem. We rarely hear about this small organ.

FIGURE 7-1 diagrams will be added in time.

(a) The reticular formation is the area which is shaded. When a stimulus enters along some neural pathway, it passes through the reticular formation, which may "wake up" the entire cortex. See Sci Am, May 1957, p. 238.

(b) This portion of the cortex plays a central role in the analysis, coding, storing of information.Sci Am Mar 70, p.67.

(c) This portion plays a major role in the formation of intentions and plans. See SciAm Mar 1970, p.67

buried deep in the brain, yet it appears to serve as a kind of managing editor for the brain. As teachers, we all need to know something about how this' editor operates and what it takes to get his cooperation. The function of the reticular formation in problem solving will be discussed, especially its role as a mediating agent between the cortical, limbic, and hypothalamic portions of the brain. Sometimes the cortex is described as the seat of thought, while the limbic and hypothalamic subsystems are characterized as the center of emotion. Apparently, the reticular formation edits the flow of messages to and from both locations. It decides which messages coming from the outside world should be responded to as "news." As teachers, we need to know how to get the reticular formation turned on for purposes of instruction. We also need to know how to carry on instruction in such a way that the coordinating, integrating, and synthesizing functions of the brain, which are necessary to effective operation in our complex society, can develop. The research suggests that without models, without opportunities to practice, and without feedback, the mental and emotional development of children will be stunted. Mental starvation, as well as physical, can produce permanent retardation.

THE RETICULAR FORMATION-MANAGING EDITOR FOR THE BRAIN

The level of complexity at which the nervous system will operate depends in part on what connections already exist in it, on its capacity to form new connections, and on its ability to integrate messages from several sources. Most of the cognitively complex processes occur in the cerebral cortex. But the cerebral cortex will be almost totally unresponsive unless a small organ much deeper in the brain "wakes up the cortex." This small organ, the ascending reticular formation, alerts the cortex for business and apparently maintains it in an "on" condition for a period of time. When the activity of the reticular formation is depressed by drugs, excessive fatigue, or sleep, the cortex ceases cognitive activity. (Figure 7-1 a.)

We can think of learning as a sequence of events that involves interactions of various organ systems of the brain in definite sequences. Messages generated by the receptors that pick up information from outside the body move toward the brain through the afferent or incoming nervous system up into the lower part of the brain. Branches from the main sensory tracts pass to the reticular formation as well as to the limbic and hypothalamic portions of the brain, the areas most closely associated with emotions. Messages flow out of the affective centers into the reticular formation. This small organ collects direct sensory input from the environment and corresponding input from the limbic and hypothalamic regions as well. All the major nerve trunks, while they go directly to the cortex, also branch into the reticular formation. Apparently it is the job of the reticular formation to keep a person conscious. While it may at times be convenient for psychologists and educators to speak about three domains -the cognitive, affective, and motor-as though they were separately manipulatable entities, the research suggests it is the nature of the interaction parts of the brain that matters. The reticular formation receives information from the limbic, hypothalamic, afferent, and cortical areas. In turn it sprays out messages, some back to the cortex and others out over the efferent paths to the muscles. The reticular formation seems to serve a kind of gate-keeping function. When sensory inputs, such as sound, arrive at the reticular formation, it apparently "decides" to which sounds to give attention. Based on its evaluation of the input, the reticular formation either wakes up or leaves the cortex in peace.

Arousing the reticular formation

The role the reticular formation plays in selective listening is not clear but has to he of great interest to teachers. If a whole array of sounds arrive at the ear, a human being can select from the array what he wishes to attend to and disregard the rest. In a classroom, for example, through all the clutter of voices that can happen at any instant, a child may be able to follow one conversation and ignore another. Both sets of sounds enter the ears but one is suppressed and treated as noise while the other passes through and is interpreted as meaningful. In addition, if several conversations go on around him at one time and he is fairly familiar with the content, a student will he able to report what transpired in more than one of the conversations. In other words, as long as there is no substantial amount of new learning that must occur, the reticular formation will apparently let both sets of messages through to the cortex. That the limbic system is also involved is illustrated by the fact that if one of the messages is emotionally fraught for the listener, e.g., some kind of murder story, then only that message will be heard. If the listener's name is mentioned in one of the conversations, his attention will be drawn to that discussion. A person's name arouses some emotion -signaling him to go on "alert" status. As the English researcher Donald Broadhent has shown, verbal instructions can have an effect on the way the reticular formation functions (Figure 7-2). Instructions can dispose a person to hear one message rather than another. In experiments on dichotic hearing, different messages are