Several physiological models have been proposed to explain hyperactivity. The high activity level has been interpreted as a parallel of an overaroused or highly aroused central nervous system (Friebergs & Douglas, 1969), as a compensatory behavior to raise the arousal of a suboptimally aroused individual via an increase in proprioceptive sensory input (Satterfield & Dawson, 1971), or a correlate of defective cortical inhibitory mechanisms (Dykman, Ackerman, Clements, & Peters, 1971).

Hyperactive children with attentional deficits have also been hypothesized to have deficiencies in cholinergic systems (Porges, 1976,  1984). Studies have indexed cholinergic activity via the parasympathetically mediated heart-rate responses. There have been reports of heart-rate responses that are incompatible with sustained attention (Porges, Walter, Korb, & Sprague, 1975). Heart-rate responses theoretically associated with sustained attention are mediated by the vagus and include slowing and stabilization of heart rate. The hyperactive child may have problems modulating the cholinergic systems and regulating parasympathetic activity. Thus, rather than observing a sympathetic dominance, the hyperactive child may have deficits in the regulation of autonomic function via the parasympathetic nervous system.

Autistic children suffer a deficit along the dimension of reactivity. There is either a hypo- or hyperreactiveness to the environment. Research dealing with physiological correlates of autism has been inconsistent. However, certain relationships have been observed that are of theoretical importance in building the link between the physiological mechanisms mediating attention and autism. Autism my have a correlate in central levels of serotonin (Boullin, Coleman, O’Brien, & Rimland, 1971). Serotonin is involved in reactivity to the environment. Since autistic children characteristically exhibit a hyporeactivity to environmental events, it might be predicted that autistic children have higher levels of serotonin than normal children.

Early discussions of sensory registration and arousal mechanisms may be traced to Pavlov (1927). He described the orienting reflex as the “What-is-it?” reflex that brings the organism closer to the source of stimulation.

The orienting reflex is not always associated with investigatory behavior, but may be related to reactive involuntary attention to changes in stimulation (Sokolov, 1963,  1969). This may range from a reaction to a change in room temperature to the dimming of light in the room. The orienting reflex, according to Sokolov, is the first response of the body to any type of stimulus and functionally “tunes” the appropriate receptor system to ensure optimal conditions for perception of the stimulus. For example, a person’s ears may prick up in order to hear a person whispering an important message.

When the orienting reflex is elicited, all activity is halted, thus allowing the individual to prepare for necessary action. As the person's body stills, the body senses have an increased sensitivity which allows them to respond adaptively to the type of stimulus that is experienced. If the stimulation is intense, the nervous system seeks to dampen the stimulus’ intensity. If the stimulus intensity is weak, yet is meaningful for the individual, the organism will work to increase its intensity (i.e., pupil dilates to increase the light influx).

The orienting reflex has both behavioral and physiological components (e.g., heart rate change, head turning, EEG activation) that occur in response to introduction of a novel stimulus. The primary behavioral component is the “orientation” of the receptor organs of the primary senses toward the source of stimulation. The initial movement of the head to facilitate audition and vision is followed by the suppression of a bodily movement to reduce the background auditory noise and to increase the visual acuity. One might then observe investigative approaches toward the stimulus (e.g., reaching) depending upon the meaning of the stimulus to the individual.

Sokolov (1963) distinguished the orienting reflex from what he labeled a defensive reflex. Just as the orienting reflex “tuned” the organism to enhance the perception of the stimulus, the defensive reflex functionally raised perceptual thresholds. The ultimate aim of the orienting reflex is to increase receptor sensitivity. However, if the stimulus reaches the critical level of intensity associated with pain, the defensive reflex develops. The defensive and orienting reflexes are generalized reactions and not limited to any specific sensory system. They differ in their ultimate objective: the orienting reflex brings the organism in contact with the stimulus, the defensive reflex limits the impact of the stimulus on the organism. The orienting and defensive reflexes are often distorted in many clinical populations with atypical sensory processing. Consider, for example, the child who is underresponsive to touch, who is slow to orient and responds only to intense tactile inputs. This child would have a weak orienting reflex while at the same time, a strong defensive reaction to tactile stimulation. Children with this problem sometimes seek intense tactile input (i.e., bump or hug other people too hard) but also respond inappropriately to painful and intense tactile stimulation (e.g., laugh or ignore it). Consider the child who is hypersensitive to movement. There is both a strong orienting and defensive reaction. This child would orient to even the slightest bit of movement and would attempt to minimize the impact of vestibular stimulation by remaining close to the ground, fixating the trunk and neck to keep the body as still as possible, and perhaps closing the eyes to eliminate vision as a vestibular receptor.

We can derive a great deal of information about an individual by learning about the specific stimuli that cause them to orient and show interest. For example, a child who does not orient or register a sensory stimulus that most individuals would normally attend to would be considered underreactive. In such a child, a much more intense stimulus would be needed to elicit orientation and interest, such as a loud alarm or blinking colored light display. Lack of orientation may also be because the stimulus is too complex or too simple. Sometimes one observes a child with cognitive delays who appears totally disinterested in a particular activity. This may be because the child has been looking at the same toy for the past hour or has seen it everyday for the past 3 months and is no longer interested in it. It could also be that the toy is too complex for the child’s cognitive level or the characteristics of the toy do not present enough sensory information for him to process its features.

Failure to habituate, therefore, may be because the individual is responding to unimportant stimuli, is not encoding relevant information for learning, or the stimuli are poorly matched to the individual’s cognitive and sensory needs. In essence, there is a defect in the orienting reflex system. Lack of habituation usually occurs when the cerebral cortex has been destroyed or suffered extensive damage. Problems with habituation are often observed in individuals with senile dementia, severe mental retardation, and certain types of schizophrenia.

The process of selective attention is intimately related to lower brain structures (e.g., reticular activating system), which filter sensory input and modulate arousal states. Processing of inputs at the cortical or conscious level can only occur if there is widespread inhibition of unrelated cortical and subcortical activity. Thus, we can learn new information from the environment more efficiently when we can effectively screen out irrelevant stimuli.

When a novel stimulus is introduced, the nervous system searches for a match or mismatch between the current stimuli and those already in the individual’s memory stores. If there is a discrepancy between what is currently experienced and prior memories (i.e., neuronal representation), the orienting reflex is elicited. The individual experiences a “This is new. What is it?” phenomenon. The orienting reflex will also occur if the stimulus is meaningful or important. In this case, the individual experiences, “I know this. It is important, and I need to respond”.

Wakefulness and sensory registration are regulated by the central core of the brainstem. An increased state of alertness is controlled by the thalamic or upper portion of the reticular formation along with nonspecific nuclei of the thalamus and diffuse thalamocortical projections. This area is affected by sympathetic activity of the nervous system and adrenalin. This is why individuals can increase their state of alertness through movement, tactile activities, or by ingesting doses of caffeine.

Broad areas of the cortex are alerted during arousal, but other parts of the cortex must be inhibited to allow for selective attention and orientation to specific sensory stimuli. This is accomplished through both cortical inhibition and feedback via cortical-reticular formation connections. In persons with ADD, it is not uncommon for them to feel flooded by competing ideas, random thoughts, or sensory distractions (e.g., noticing sounds in the environment when trying to concentrate). This is because they have difficulty inhibiting cortical feedback and reticular formation activity that does not relate to the task at hand.

Sensory registration and orientation to sensory stimulation including smell, taste, touch, and interoception are mediated by the limbic system, which includes the hippocampus, amygdala, and hypothalamus. The limbic system registers qualitative aspects of a sensory stimulus rather than precise discriminative sensory information, such as specific object traits. The hypothalamus and limbic system play an important role in things like feeding, fight or flight, mating, and emotion-provoking situations. These structures also help regulate homeostatic functions necessary for self-preservation and approach and withdrawal. This is the part of the nervous system that is affected in individuals with distorted sensory regulation systems (i.e., sensory hyper or hyposensitivities). For example, the hyperreactive person may perceive touch from others as highly aversive and too arousing. He might avoid physical touch from others and may associate negative emotions with affection or physical contact.

One of the limbic system’s roles is to modulate, dampen, and regulate fluctuations in attentional responses by coordinating autonomic, somatic, and behavioral responses. For example, during a demanding and novel attentional task, our heart rate usually quickens, but our motor activity quiets, thus maintaining a level of arousal in one system that is balanced with inhibition in another to allow for optimal learning. The limbic system helps discriminate objects in time and space. It processes novelty, change, and inconsistencies in stimulus features. It is concerned with pleasure-pain, immediacy, approach-avoidance, and fight or flight. It also helps in discriminating what properties of a given stimulus are shared with others rather than processing the specific properties of objects (e.g., texture, shape).

The hippocampus has several important functions. It helps maintain attention, compares new sensory inputs with stored information, aids in storage and retrieval of memory stores, and inhibits the reticular formation when a stimulus is familiar. The hippocampus is sensitive to intensity gradients (e.g., loud/soft, strong/weak, fast/slow) and also facilitates transmission of afferent input to the amygdala. When the hippocampus is damaged, the individual will have difficulty detecting and differentiating novel and familiar stimuli, may be slow to habituate, and will have a strong preference for familiar activities. The person may have a strong dislike for change and need routines to be the same, engage in ritualistic kinds of behaviors, be overattentive to irrelevant stimuli, or resist exploring new things. This type of person may need many repetitions before they can respond appropriately to a new situation or activity and typically it takes them longer to generalize newly learned skills.

The amygdala is a forebrain structure in the temporal lobe containing many nuclei that interconnect with the hypothalamus, hippocampal formation, and thalamus. The amygdala registers and synthesizes incoming novel sensory inputs and has a role in cessation of motor activity, thus playing an important role in both arousal and on-task attention. When the amygdala is damaged, the individual is apt to have problems arousing to novel stimuli, and integrating appropriate emotional responses to sensory inputs, usually overresponding. They may not be able to sustain on-task attention and tend to be hyperactive or restless, and they may show fear or anxiety in novel situations. When there are combined lesions of the hippocampus and amygdala, the person often has memory problems and amnesia similar to that observed in patients suffering from Korsakoff’s psychosis.

Persons with poor prefrontal cortex functioning are apt to have poor impulse control, have difficulty learning from their own mistakes, and have poor problem-solving, planning, and organizational skills. Deficits in the dorsal lateral prefrontal cortex are apt to result in a person having high distractibility, a short attention span, apathy, and decreased verbal expression. Other problems include hyperactivity, procrastination, disorganization, short-term memory problems, and poor judgment. The person may also misperceive situations and have trouble learning from their own experiences. Deficits in the inferior orbital cortex can contribute to poor impulse control and mood control problems due to the connections with the limbic system.

At first Noah had difficulty tolerating his mother playing near him in his space and in sharing toys with her. He would frequently turn his back to her or tell her that she was not allowed to touch the toys. I urged Mrs. S. to simply engage with Noah on a verbal level (e.g., “Look at the cars riding down the road. I wonder where they’re going?”). Sometimes I provided Mrs. S. with props, such as a toy telephone or a walkie-talkie that she could use in calling Noah to find out what he was doing in his play. Noah liked this and began initiating phone calls back to his mother to tell her about his play. I encouraged Mrs. S. to use other props, such as binoculars, periscopes, or long tubes to watch Noah, thus highlighting the connection between them. We also incorporated dress-ups, such as a colorful clown wig, fireman or policeman hats, and construction worker tools for both mother and child to wear. Noah loved playing with these props and would elaborate on their use in his play. At times Noah sought being inside enclosed spaces, such as retreating to the pup tent filled with pillows or climbing into a bin of plastic balls. It appeared that he did this to regroup when the stimulation of the interaction became too much for him. At other times he wanted his mother to join him in the pup tent. Mrs. S. was sensitive to Noah’s cues and seemed to understand that he might need some time and space to himself after playing in close proximity to her. When he wanted to retreat, it was never for more than a few minutes and almost always, he would call to his mother and ask her questions that incorporated a play idea (i.e., “Are there any bad guys out there?).

As we looked for ways to help Noah remain engaged and attentive during the play, we found that he did best when the play materials were highly visual and provided proprioceptive input. Noah loved being a fireman but enacting this play idea was short-lived unless we made the “fire” be shiny red paper shakers and gave him a vibrating tubing for the hose. He also loved taking trains places but would usually become self-absorbed in this task, resisting his mother joining him as he pushed the trains. To help him vary his play and to encourage him to interact with his mother, we tried setting up obstacles, such as a dump truck stuck on the train tracks, or a toy giraffe who persistently asked for a ride on the train to get to his friend, the dinosaur’s, house. As Noah loved animals and trucks, he was intrigued with these play ideas and eventually allowed Mrs. S. to enter his play.

Noah’s play was often more interactive when it involved the idea of constructing an enclosed space, such as building a fort with large foam blocks. Gradually Noah began wanting to play out stories like the “Three Little Pigs,” asking his mother to be the big bad wolf. Noah would take little pig puppets into the house and would gleefully enact the story with his mother. I urged Mrs. S. to vary the story and make mistakes on purpose so that he would be forced to elaborate on his play ideas. When she did this, Noah would say, “No, that’s not right! It’s not a big bad crocodile, it’s a wolf” or “No, he doesn’t break down the house with a hammer, he blows it down.”

As the therapy sessions entered the third month of treatment, Noah’s play changed in content and process. His behavior at home had improved dramatically. He was sitting for meals, listening to his parents, complying with most daily routines, and transitions from one activity to the next were going smoothly. During this month of therapy, Noah began to play in the dollhouse, playing out how the house was all messed up. He would knock furniture around, saying that it was getting hit by a hurricane. This idea of chaos versus order was played out in other play scenarios. He often constructed play that involved the dolls going to sleep, waking up, then going to school. While the children were at school, animals came to the house to play with the family dog. When the parents and children came home, they found animals playing in the house who had messed up the furniture, jumped on the beds, and put food all over the place. Mrs. S. felt that his play reflected his continuing difficulties with impulse control, but she was encouraged that he could express it through play rather than becoming disruptive or impulsive in everyday routines.

As Noah loved stories, we spent a part of the session focusing on problem solving around impulse control using story telling. For example, one story he particularly liked was about a boy who swam in a pond every day, but one day after a big storm, a dolphin got into the pond from the ocean. The dolphin kept taking up the whole pond, jumping and splashing so hard that the boy couldn’t swim in the pond. Noah came up with several ideas to help solve the problem. He decided that we should first teach the dolphin tricks when the boy could ride on the dolphin’s back, then he lured the dolphin back to the ocean and put a pen between the ocean and pond so that the dolphin wouldn’t get confused and come back to the pond. We also played games that required him and his mother to work slowly and carefully, otherwise the game would be ruined. Building with magnets to make a circus, constructing houses with Legos, and games, such as “Don’t Spill the Beans” helped him learn how to do this.

By the second month of therapy, Mrs. S. was able to talk about her need to control Noah. For instance, if he wanted to brush his teeth himself, she felt she had to finish it for him. Mr. and Mrs. S. were asked to pick a few things that mattered most to them at home where rules counted, that is, if Noah wants to eat, he must sit in his chair. Positive reinforcement was used as much as possible. For example, wearing the seat belt in the car either yielded a ride to the park or a lollipop. It was stressed that in other activities, Mr. and Mrs. S. should let Noah take the initiative and do it his way. Practice setting consistent and firm limits was part of the parent guidance. For instance, Mr. and Mrs. S. practiced how to be firm with Noah, saying “No throwing” while looking sternly. They often gave Noah elaborate reasons why he should not throw toys instead of instituting a simple rule. We also implemented a behavioral chart that reinforced sitting for meals, using “walking feet” in the house and sitting in his bean bag chair for quiet play. If Noah could do these things, he got a reward of going to the library to get a new book, TV time, or a visit to the “mommy treat store.” Within a few weeks, considerable improvement was noted in Noah’s attention span and behavioral difficulties, in large part because his parents were diligent in following through on the program.

Noah’s treatment seemed to be successful for several reasons. Working through the parent–child relationship using child-centered activity helped him to organize his attention while engaged in interactions with his parents. Noah was able to make use of environmental modifications (e.g., sitting in enclosed spaces), as well as sensory mediums (e.g., heavy objects) to organize himself. He was able to learn how to tolerate frustration, make transitions in activities, accept structure and limits, modulate his activity level, and contain his impulses during interactions with persons and objects. The child-centered activity helped Noah to be better able to express emotional themes related to separation, autonomy, and power and control. His ability to express these needs to his mother through play and her sensitivity in responding to him were important in promoting his sense of mastery and control.