A chapter from
Textbook of Neurofeedback, EEG Biofeedback, qEEG and Brain Self Regulation
I. Introduction.
2. The brain functions as a communication system.
3. The brain functions as a gland, with neurotransmitters and neuropeptides.
4. The brain functions as a system of adaptation.
5. The brain controls emotions. Mood related to patho-physiology.
6. The brain controls activity and behavior. Hypo-activity and hyper-activity.
7. The nervous system is built on stimulus-response mechanisms.
8. Biofeedback as a treatment modality in neuropsychiatry.
9. Biofeedback as a treatment modality in restorative neurology.
1. INTRODUCTION
People commonly ask the questions : "Why?", "How does a thing work?" and "How can I fix it?". I do not attempt to answer "Why?" because it is a metaphysical question. Much of this article answers the question of "How can I fix it?".
I shall mainly describe "How does the brain work?" which I freely acknowledge is an immodest goal.
The nervous system is built upon a living network of feedback, constantly adapting to the environment, both the internal and the external. The prefix"bio" in biofeedback is semantically unnecessary since we are dealing with systems during life. However, because of the historical use of "biofeedback" as a treatment modality the term can be accepted.
Biofeedback is an important technique in the wide spectrum of behavioral medicine. Behavior is the motor output of the nervous system which depends upon the conscious and unconscious reception and acceptance of stimuli by an individual. It is the response to a continuous stream of stimuli in the waking and the sleeping state. Biofeedback professionals learn the art of encouraging self-awareness both of themselves and of their patients, in order for perception of stimuli to be changed if desired.
Therefore we need to become more self-aware of the physiology that generates our behavior. We need to harness our feedback forces, and to use the inherent physiological mechanisms of feedback to the best advantage of ourselves and of those whom we contact.
Behavioral responses can be modified by the way the individual perceives these incoming stimuli. Similar stimuli are experienced differently by different people, and they also vary according to the actual psycho-physiological state of the individual, including their age and experiences.
A.R. Luria in his classic book "Higher Cortical Function in Man" analysed "the reflex mechanisms by means of which the organism maintains its equilibrium with the environment" and "the problem of the cerebral mechanisms of mental activity". Replace the word "reflex" by "biofeedback" and we see how we are perpetually studying these mechanisms.
For an excellent review of the central autonomic network (CAN), with its functional organization and dysfunction, the reader is referred to the article by Eduardo Benarroch (1993), (see Fig 1).
2. THE BRAIN AS A COMMUNICATION SYSTEM
The brain functions as a system for communication over the entire body. The nervous system consists of a CENTRAL part (the brain and the spinal cord) and a PERIPHERAL part which comprises the nerves that arises from the brain and spinal cord. These nerves supply the special senses, the musculature and the sensation of the trunk and the four limbs.
This chapter deals with the central nervous system (CNS). It is a bilateral and in many ways symmetrical group of structures consisting of 6 parts: (1) the Spinal cord; (2) the Brain stem subdivided into 3 regions, the midbrain, the pons and the medulla; (3) the Cerebellum, important for modulating and co-ordinating motor movement together with (4) the Basal ganglia, (the caudate nucleus, putamen and globus pallidus); (5) the Diencephalon (the thalamus, hypothalamus, subthalamus, and epithalamus) and (6) the Cerebral Hemispheres capped by the cerebral cortex or rind with higher perceptual cognitive and motor functions, (Kandel). (see fig 2). The brain weighs 3 lbs. The spinal cord is like a tail arising from the base of the brain and its thickness averages that of a human finger.
Broadly speaking the tasks of the brain can be divided into three categories:
(1) the RECEPTION OF STIMULI (this is the sensory system);
(2) the association of stimuli and the analysis or PERCEPTION OF INCOMING STIMULI; and (
3) the MOTOR RESPONSE to those stimuli. These motor responses summate so as to constitute the behavior of the individual. At the cellular level, sensory signals are transformed into motor acts.
(1) The RECEPTION OF STIMULI by the brain occurs via the AFFERENT PATHWAYS FOR SENSATION. (The term"afferent" indicates travelling towards the brain, and "efferent" travelling away from the brain.) The pathways for light touch, (tickle), pain, pressure, heat, cold and vibration from the periphery to the cerebral cortex are well-known and they do not vary significantly. It is the conscious PERCEPTION by the individual of these stimuli (when they reach the appropriate area of the cerebral cortex) which varies constantly throughout life.
In order to prevent overloading of the individual by a continous stream of stimuli, the nervous system has developed a variety of methods of INHIBITION. Inhibition is an important neurological concept for biofeedback professionals since learning how to inhibit sensations, thoughts or behavior is basic in biofeedback training. Inhibition as applied to synaptic transmission refers to an active process by which excitatory transmission is prevented. Inhibition occurs in the CNS both before and after the synapse ("pre-synaptic" and "post-synaptic"). A major pre-synaptic neurotransmitter, which is inhibitory in many processes, is gamma-amino-butyric-acid (GABA). In the thalamus (its nucleus is the main way-station for sensation) there is both pre- and post-synaptic inhibition. At higher levels in the brain, both in the cerebellum and in the cerebral cortex, inhibition is mainly post-synaptic.
Inhibition can be directed from the cerebral cortex. Efferent pathways from the sensori-motor cortex excite thalamo-cortical relay cells. By exerting inhibition the cerebral cortex is able to block the synapses and thus to protect itself from being stimulated by cutaneous stimuli; it can neglect these stimuli. This happens for example when one is deep in thought, preoccupied with an experience or intensely involved in carrying out an action. Counter-irritation to relieve pain acts in this way. Discharges from the cerebral cortex down the pyramidal tracts and other pathways may exert an inhibitory blockage at the relays in the spino-cortical pathways. This can inhibit unwanted motor movements.
INHIBITORY FUNCTIONS OF THE CEREBELLUM.
The cerebellum is the great "smoother" of all motor activities. The Purkinje cells are large nerve cells in the cerebellar cortex. The unique feature of the cerebellar cortex is that its output is expressed entirely by the inhibitory Purkinje cells.
Nowhere else in the brain is inhibition so dominant. How can information be conveyed effectively in this negative manner? Because this inhibitory action is exerted on nuclear cells that have a strong background discharge.
Eccles gives the analogy of the sculpture of stone. A sculptor has a block and achieves form by "taking away" stone through chiselling. Similarly the Purkinje cells of the cerebellum achieve form in the nuclear cell discharge by taking away from the background discharges through the process of inhibition.
(2) The association of stimuli and the analysis or PERCEPTION OF INCOMING STIMULI is carried out in the cerebral hemispheres. Here memory, judgement, thought association, verbal and non-verbal communication, the emotional coloring of stimuli all combine to create the personal interpretation of on-going stimuli. This is the meeting-ground which regulates the psycho-physiology of the individual.
(3) THE MOTOR RESPONSE TO THE STIMULI. This is the output of the brain, the efferent system, via the pyramidal, extra-pyramidal and non-pyramidal pathways.
These responses require exquisite MOTOR COORDINATION.
The CEREBELLUM is concerned with the reliable and regulated control of movement. The cerebellum is the part of the brain which through the process of evolution has come to function as a special computer by handling all the complex inputs from receptors or from other parts of the brain. The articulation of speech is subserved by cerebellar mechanisms.
Let us visualize the neural events in the cerebro-cerebellar circuits during a skilled action, such as running a machine at work or playing the piano. There will be initially a motor command with a preprogramming of the movements by circuits in the association cortex, cerebellum, basal ganglia and thalamic nuclei. The learned skills are mobilized and the discharge leads on to the action impulses in the pyramidal tract, with the consequent report of the discharge to the part of the cerebellar cortex receiving and projecting both to the cerebrum and the spinal cord. Cerebral"willing" of a muscle movement sets in train neural events that lead to the discharge of pyramidal cells.
There is a sequence of neuronal events, a chain reaction, such that one part is called into operation (in the temporal or time sense) and this leads other parts to go into action which generates further activity . Since, however, all areas of the brain are constantly (and therefore concurrently) active, many elements are carrying out their own intrinsic activities (cross-talks between the cells) which are not apparent to an outside observer; these do not impinge on the consciousness of the individual concerned. It is clear, therefore, that a good deal of cerebral activity goes unheeded by the originator and all observers.
Biofeedback treatment is based on learning. How does the brain as the organ of communication bring about learning?
The process of learning consists of excluding from consciousness all stimuli except the one which the individual chooses to focus upon, and to which his attention is directed. The acquisition of new data thus involves a process of selective listening and consists mainly of rejection or ignoring of stimuli which are nonrelevant at that time.
Biofeedback consists of acquiring a technique for selective "listening" to a particular set of stimuli, which may come from the external environment or from inside the individual's own body (internal environment) . The purpose of the technique is for the student to have the ability to regulate psycho-physical function himself. In order to acquire and to teach this technique, we have to know, first, the GEOGRAPHY OF SPECIALIZED FUNCTIONING, meaning the localization within the brain of neurons with specialized function. These neurons in different parts of the brain vary greatly one from another. For example they vary in size as a petunia varies from an oak tree, (Stevens). Second, we have to understand the interconnections (neural connections) or microstructural changes in SYNAPSES, linkages or pathways of the brain, because this gives a basis of the HOW of behavior, both of the patient and of ourselves. Third, we have to understand the concept of EXCITATION and INHIBITION. The neurons are either excitatory or inhibitory and/or secretory. When two parts of the brain (two neuronal populations) interact, they may each exert an excitatory or an inhibitory effect.
A neuronal impulse may release a neurotransmitter which excites or inhibits. If one part fails to act, there is uncontrolled or deafferented functioning of neurones, because they are lacking their accustomed stimulation or input.
NEURONAL FUNCTION.
Neurons have four main functions: (1) they respond to specific neurotransmitters by altering membrane permeability to common ions (sodium, chloride, potassium, calcium); (2) they conduct electrical impulses; (3) they secrete transmitters (see below in "Neurotransmitter"); (4) they communicate with other post-synaptic cells by the process of synaptic transmission.
Neurons are able to respond and act as "receptors"; this is because their intrinsic membranes (coverings) contain proteins which can receive messages and are therefore called receptors. The membranes of different neurons contain different receptors.. These receptors are protein-complexes bound in the intrinsic membrane of the neuron.
3. THE BRAIN AS A GLAND
When we add together the concepts of the brain as the organ for communication and the brain as a gland, secreting chemicals, we see that the sensory messages that arrive at the brain from the periphery are being continuously changed, altered, modified, censored, embellished, intensified or inhibited by NEUROTRANSMITTERS. A transmitter is a chemical substance that is released synaptically by one neuron and that affects another cell (neuron or effector organ) in a specific manner. However, a given transmitter does not always open the same ionic gates or bring about the same biochemical change in the postsynaptic neuron; the receptor determines whether the synapse will be excitatory or inhibitory.
These transmitters act at the neuro-muscular junctions, the interneuronal junctions and the sensory way-stations, and they are either repressed or further attended to and analysed according to the state of the "receiving" cortex. The incoming sensations are matched with previous experiences. The brain can discard anything "foreign" in the same way that foreign substances like grafts, bacteria or other non-self substances are rejected by the tissues which represent the "self". Some nerve cell receptors have been found to be isomers of immune cell receptors.
SYNAPTIC TRANSMISSION. There are four biochemical steps in synaptic transmission: (1) synthesis of the neurotransmitter substance; (2) release of transmitter into the synaptic cleft; (3) binding of transmitter to the postsynaptic receptor, and (4) removal or destruction of the transmitter substance, (Schwartz).
There are eight substances which are the original classical neurotransmitters: Acetylcholine, the 4 biogenic amines: Dopamine, Histamine, Nor-epinephrine (the locus caeruleus is rich in nor-epinephrine), and Serotonin (5-hydroxy-tryptamine) ; and 3 amino-acids: Gamma-amino-butyric acid (GABA), Glycine and Glutamate.
NEUROPEPTIDES. Some neurotransmitters are, chemically, neuropeptides.
Neuroactive peptides or neuropeptides have been found to be localized in neurons. More than 50 neuropeptides have now been isolated and arranged in a chemical sequence. They range is size from small peptides (two amino acids joined by a single peptide bond) to a large molecule such as corticotropin-releasing-factor (CRF) which is comprised of 41 amino acids.(Nemeroff). The amino acids arranged in chains include Glycine, Alanine, Leucine, Aspartine and Arginine.
These neuropeptides act as hormones in some tissues, (a hormone is a chemical messenger, a substance released at considerable distance from its intended site of action); and in other tissues these peptides act as neurotransmitters
( a neurotransmitter is released directly onto the site of the intended action).
Neuropeptides are important in the field of biofeedback because their action is closely related to the psycho-physical state of the individual.
Certain neuropeptides are involved in the perception of pain, pleasure, fear, depression and other emotions. Others are involved in the control of blood pressure, reproduction, and the mobilizing of energy. Some can be termed neuromodulators because they are substances that modulate the action of classical neurotransmitters, (the first 25 or so neurotransmitters to be isolated), but the field is increasing so rapidly that terms change their exact meaning.
The brain, functioning as a gland secreting chemicals, regulates our psycho-physical state through many systems, including the gastro-intestinal, the cardio-vascular and the immune systems. Many brain areas are particularly involved, including the hypothalamus. the pituitary, and the amygdala. We shall discuss these biochemical factors as they relate to mood and behavior.
First we review the brain areas identified as specially important.
The HYPOTHALAMUS.
The hypothalamus is a minute collection of nuclei situated just below the thalamus. These nuclei are distinguished microscopically, and they include the median eminence, the peri-and para-ventricular nuclei, the preoptic nuclei, the arcuate nucleus and many others.
HYPOTHALAMIC-RELEASING HORMONES include Thyrotropin-releasing hormone (TRH), Luteinizing hormone (LH), and somatostatin (growth hormone release-inhibiting factor, SRIF).
The PITUITARY. The pituitary is the pea-like body sitting in the pituitary fossa at the base of the skull. PITUITARY PEPTIDES include Adrenocorticotropin (ACTH), Beta-Endorphin, Vasopressin and Oxytocin. The hypothalamic-pituitary-adrenal axis is central to many aspects of the stress response.
The AMYGDALA. (plural for amygdalum). The amygdalum is a nucleus the shape of an almond situated deep in each temporal lobe. The two nuclei constitute the amygdala and are part of the limbic system, the so-called affective brain, associated with emotionally-based behavior. The amygdala within the limbic system connects to the cerebral cortex, to the thalamus and hypothalamus, and to the brainstem and spinal cord. The amygala is important for the mediation of normal responses to fear-evoking or anxiety-producing stimuli. Epileptic seizures where the abnormal neuronal discharge involves the amygdalum can be manifested by severe sensations of fear and memories of events full of fear. Autonomic changes can accompany this fear with increases in heart rate and blood pressure, dialation of the pupils and pallor. "A majority of the peptides that have been localised with neurons of the brain are found within either neuronal cells bodies or terminals of the amygdala" (Gray). These include cortocotropin-releasing factor (CRF), neurotensin, Enkephalin, Somatostatin and Substance P.
Next we review the systems where neuropeptides are particularly involved.
Textbook of Neurofeedback, EEG Biofeedback, qEEG and Brain Self Regulation
I. Introduction.
2. The brain functions as a communication system.
3. The brain functions as a gland, with neurotransmitters and neuropeptides.
4. The brain functions as a system of adaptation.
5. The brain controls emotions. Mood related to patho-physiology.
6. The brain controls activity and behavior. Hypo-activity and hyper-activity.
7. The nervous system is built on stimulus-response mechanisms.
8. Biofeedback as a treatment modality in neuropsychiatry.
9. Biofeedback as a treatment modality in restorative neurology.
1. INTRODUCTION
People commonly ask the questions : "Why?", "How does a thing work?" and "How can I fix it?". I do not attempt to answer "Why?" because it is a metaphysical question. Much of this article answers the question of "How can I fix it?".
I shall mainly describe "How does the brain work?" which I freely acknowledge is an immodest goal.
The nervous system is built upon a living network of feedback, constantly adapting to the environment, both the internal and the external. The prefix"bio" in biofeedback is semantically unnecessary since we are dealing with systems during life. However, because of the historical use of "biofeedback" as a treatment modality the term can be accepted.
Biofeedback is an important technique in the wide spectrum of behavioral medicine. Behavior is the motor output of the nervous system which depends upon the conscious and unconscious reception and acceptance of stimuli by an individual. It is the response to a continuous stream of stimuli in the waking and the sleeping state. Biofeedback professionals learn the art of encouraging self-awareness both of themselves and of their patients, in order for perception of stimuli to be changed if desired.
Therefore we need to become more self-aware of the physiology that generates our behavior. We need to harness our feedback forces, and to use the inherent physiological mechanisms of feedback to the best advantage of ourselves and of those whom we contact.
Behavioral responses can be modified by the way the individual perceives these incoming stimuli. Similar stimuli are experienced differently by different people, and they also vary according to the actual psycho-physiological state of the individual, including their age and experiences.
A.R. Luria in his classic book "Higher Cortical Function in Man" analysed "the reflex mechanisms by means of which the organism maintains its equilibrium with the environment" and "the problem of the cerebral mechanisms of mental activity". Replace the word "reflex" by "biofeedback" and we see how we are perpetually studying these mechanisms.
For an excellent review of the central autonomic network (CAN), with its functional organization and dysfunction, the reader is referred to the article by Eduardo Benarroch (1993), (see Fig 1).
2. THE BRAIN AS A COMMUNICATION SYSTEM
The brain functions as a system for communication over the entire body. The nervous system consists of a CENTRAL part (the brain and the spinal cord) and a PERIPHERAL part which comprises the nerves that arises from the brain and spinal cord. These nerves supply the special senses, the musculature and the sensation of the trunk and the four limbs.
This chapter deals with the central nervous system (CNS). It is a bilateral and in many ways symmetrical group of structures consisting of 6 parts: (1) the Spinal cord; (2) the Brain stem subdivided into 3 regions, the midbrain, the pons and the medulla; (3) the Cerebellum, important for modulating and co-ordinating motor movement together with (4) the Basal ganglia, (the caudate nucleus, putamen and globus pallidus); (5) the Diencephalon (the thalamus, hypothalamus, subthalamus, and epithalamus) and (6) the Cerebral Hemispheres capped by the cerebral cortex or rind with higher perceptual cognitive and motor functions, (Kandel). (see fig 2). The brain weighs 3 lbs. The spinal cord is like a tail arising from the base of the brain and its thickness averages that of a human finger.
Broadly speaking the tasks of the brain can be divided into three categories:
(1) the RECEPTION OF STIMULI (this is the sensory system);
(2) the association of stimuli and the analysis or PERCEPTION OF INCOMING STIMULI; and (
3) the MOTOR RESPONSE to those stimuli. These motor responses summate so as to constitute the behavior of the individual. At the cellular level, sensory signals are transformed into motor acts.
(1) The RECEPTION OF STIMULI by the brain occurs via the AFFERENT PATHWAYS FOR SENSATION. (The term"afferent" indicates travelling towards the brain, and "efferent" travelling away from the brain.) The pathways for light touch, (tickle), pain, pressure, heat, cold and vibration from the periphery to the cerebral cortex are well-known and they do not vary significantly. It is the conscious PERCEPTION by the individual of these stimuli (when they reach the appropriate area of the cerebral cortex) which varies constantly throughout life.
In order to prevent overloading of the individual by a continous stream of stimuli, the nervous system has developed a variety of methods of INHIBITION. Inhibition is an important neurological concept for biofeedback professionals since learning how to inhibit sensations, thoughts or behavior is basic in biofeedback training. Inhibition as applied to synaptic transmission refers to an active process by which excitatory transmission is prevented. Inhibition occurs in the CNS both before and after the synapse ("pre-synaptic" and "post-synaptic"). A major pre-synaptic neurotransmitter, which is inhibitory in many processes, is gamma-amino-butyric-acid (GABA). In the thalamus (its nucleus is the main way-station for sensation) there is both pre- and post-synaptic inhibition. At higher levels in the brain, both in the cerebellum and in the cerebral cortex, inhibition is mainly post-synaptic.
Inhibition can be directed from the cerebral cortex. Efferent pathways from the sensori-motor cortex excite thalamo-cortical relay cells. By exerting inhibition the cerebral cortex is able to block the synapses and thus to protect itself from being stimulated by cutaneous stimuli; it can neglect these stimuli. This happens for example when one is deep in thought, preoccupied with an experience or intensely involved in carrying out an action. Counter-irritation to relieve pain acts in this way. Discharges from the cerebral cortex down the pyramidal tracts and other pathways may exert an inhibitory blockage at the relays in the spino-cortical pathways. This can inhibit unwanted motor movements.
INHIBITORY FUNCTIONS OF THE CEREBELLUM.
The cerebellum is the great "smoother" of all motor activities. The Purkinje cells are large nerve cells in the cerebellar cortex. The unique feature of the cerebellar cortex is that its output is expressed entirely by the inhibitory Purkinje cells.
Nowhere else in the brain is inhibition so dominant. How can information be conveyed effectively in this negative manner? Because this inhibitory action is exerted on nuclear cells that have a strong background discharge.
Eccles gives the analogy of the sculpture of stone. A sculptor has a block and achieves form by "taking away" stone through chiselling. Similarly the Purkinje cells of the cerebellum achieve form in the nuclear cell discharge by taking away from the background discharges through the process of inhibition.
(2) The association of stimuli and the analysis or PERCEPTION OF INCOMING STIMULI is carried out in the cerebral hemispheres. Here memory, judgement, thought association, verbal and non-verbal communication, the emotional coloring of stimuli all combine to create the personal interpretation of on-going stimuli. This is the meeting-ground which regulates the psycho-physiology of the individual.
(3) THE MOTOR RESPONSE TO THE STIMULI. This is the output of the brain, the efferent system, via the pyramidal, extra-pyramidal and non-pyramidal pathways.
These responses require exquisite MOTOR COORDINATION.
The CEREBELLUM is concerned with the reliable and regulated control of movement. The cerebellum is the part of the brain which through the process of evolution has come to function as a special computer by handling all the complex inputs from receptors or from other parts of the brain. The articulation of speech is subserved by cerebellar mechanisms.
Let us visualize the neural events in the cerebro-cerebellar circuits during a skilled action, such as running a machine at work or playing the piano. There will be initially a motor command with a preprogramming of the movements by circuits in the association cortex, cerebellum, basal ganglia and thalamic nuclei. The learned skills are mobilized and the discharge leads on to the action impulses in the pyramidal tract, with the consequent report of the discharge to the part of the cerebellar cortex receiving and projecting both to the cerebrum and the spinal cord. Cerebral"willing" of a muscle movement sets in train neural events that lead to the discharge of pyramidal cells.
There is a sequence of neuronal events, a chain reaction, such that one part is called into operation (in the temporal or time sense) and this leads other parts to go into action which generates further activity . Since, however, all areas of the brain are constantly (and therefore concurrently) active, many elements are carrying out their own intrinsic activities (cross-talks between the cells) which are not apparent to an outside observer; these do not impinge on the consciousness of the individual concerned. It is clear, therefore, that a good deal of cerebral activity goes unheeded by the originator and all observers.
Biofeedback treatment is based on learning. How does the brain as the organ of communication bring about learning?
The process of learning consists of excluding from consciousness all stimuli except the one which the individual chooses to focus upon, and to which his attention is directed. The acquisition of new data thus involves a process of selective listening and consists mainly of rejection or ignoring of stimuli which are nonrelevant at that time.
Biofeedback consists of acquiring a technique for selective "listening" to a particular set of stimuli, which may come from the external environment or from inside the individual's own body (internal environment) . The purpose of the technique is for the student to have the ability to regulate psycho-physical function himself. In order to acquire and to teach this technique, we have to know, first, the GEOGRAPHY OF SPECIALIZED FUNCTIONING, meaning the localization within the brain of neurons with specialized function. These neurons in different parts of the brain vary greatly one from another. For example they vary in size as a petunia varies from an oak tree, (Stevens). Second, we have to understand the interconnections (neural connections) or microstructural changes in SYNAPSES, linkages or pathways of the brain, because this gives a basis of the HOW of behavior, both of the patient and of ourselves. Third, we have to understand the concept of EXCITATION and INHIBITION. The neurons are either excitatory or inhibitory and/or secretory. When two parts of the brain (two neuronal populations) interact, they may each exert an excitatory or an inhibitory effect.
A neuronal impulse may release a neurotransmitter which excites or inhibits. If one part fails to act, there is uncontrolled or deafferented functioning of neurones, because they are lacking their accustomed stimulation or input.
NEURONAL FUNCTION.
Neurons have four main functions: (1) they respond to specific neurotransmitters by altering membrane permeability to common ions (sodium, chloride, potassium, calcium); (2) they conduct electrical impulses; (3) they secrete transmitters (see below in "Neurotransmitter"); (4) they communicate with other post-synaptic cells by the process of synaptic transmission.
Neurons are able to respond and act as "receptors"; this is because their intrinsic membranes (coverings) contain proteins which can receive messages and are therefore called receptors. The membranes of different neurons contain different receptors.. These receptors are protein-complexes bound in the intrinsic membrane of the neuron.
3. THE BRAIN AS A GLAND
When we add together the concepts of the brain as the organ for communication and the brain as a gland, secreting chemicals, we see that the sensory messages that arrive at the brain from the periphery are being continuously changed, altered, modified, censored, embellished, intensified or inhibited by NEUROTRANSMITTERS. A transmitter is a chemical substance that is released synaptically by one neuron and that affects another cell (neuron or effector organ) in a specific manner. However, a given transmitter does not always open the same ionic gates or bring about the same biochemical change in the postsynaptic neuron; the receptor determines whether the synapse will be excitatory or inhibitory.
These transmitters act at the neuro-muscular junctions, the interneuronal junctions and the sensory way-stations, and they are either repressed or further attended to and analysed according to the state of the "receiving" cortex. The incoming sensations are matched with previous experiences. The brain can discard anything "foreign" in the same way that foreign substances like grafts, bacteria or other non-self substances are rejected by the tissues which represent the "self". Some nerve cell receptors have been found to be isomers of immune cell receptors.
SYNAPTIC TRANSMISSION. There are four biochemical steps in synaptic transmission: (1) synthesis of the neurotransmitter substance; (2) release of transmitter into the synaptic cleft; (3) binding of transmitter to the postsynaptic receptor, and (4) removal or destruction of the transmitter substance, (Schwartz).
There are eight substances which are the original classical neurotransmitters: Acetylcholine, the 4 biogenic amines: Dopamine, Histamine, Nor-epinephrine (the locus caeruleus is rich in nor-epinephrine), and Serotonin (5-hydroxy-tryptamine) ; and 3 amino-acids: Gamma-amino-butyric acid (GABA), Glycine and Glutamate.
NEUROPEPTIDES. Some neurotransmitters are, chemically, neuropeptides.
Neuroactive peptides or neuropeptides have been found to be localized in neurons. More than 50 neuropeptides have now been isolated and arranged in a chemical sequence. They range is size from small peptides (two amino acids joined by a single peptide bond) to a large molecule such as corticotropin-releasing-factor (CRF) which is comprised of 41 amino acids.(Nemeroff). The amino acids arranged in chains include Glycine, Alanine, Leucine, Aspartine and Arginine.
These neuropeptides act as hormones in some tissues, (a hormone is a chemical messenger, a substance released at considerable distance from its intended site of action); and in other tissues these peptides act as neurotransmitters
( a neurotransmitter is released directly onto the site of the intended action).
Neuropeptides are important in the field of biofeedback because their action is closely related to the psycho-physical state of the individual.
Certain neuropeptides are involved in the perception of pain, pleasure, fear, depression and other emotions. Others are involved in the control of blood pressure, reproduction, and the mobilizing of energy. Some can be termed neuromodulators because they are substances that modulate the action of classical neurotransmitters, (the first 25 or so neurotransmitters to be isolated), but the field is increasing so rapidly that terms change their exact meaning.
The brain, functioning as a gland secreting chemicals, regulates our psycho-physical state through many systems, including the gastro-intestinal, the cardio-vascular and the immune systems. Many brain areas are particularly involved, including the hypothalamus. the pituitary, and the amygdala. We shall discuss these biochemical factors as they relate to mood and behavior.
First we review the brain areas identified as specially important.
The HYPOTHALAMUS.
The hypothalamus is a minute collection of nuclei situated just below the thalamus. These nuclei are distinguished microscopically, and they include the median eminence, the peri-and para-ventricular nuclei, the preoptic nuclei, the arcuate nucleus and many others.
HYPOTHALAMIC-RELEASING HORMONES include Thyrotropin-releasing hormone (TRH), Luteinizing hormone (LH), and somatostatin (growth hormone release-inhibiting factor, SRIF).
The PITUITARY. The pituitary is the pea-like body sitting in the pituitary fossa at the base of the skull. PITUITARY PEPTIDES include Adrenocorticotropin (ACTH), Beta-Endorphin, Vasopressin and Oxytocin. The hypothalamic-pituitary-adrenal axis is central to many aspects of the stress response.
The AMYGDALA. (plural for amygdalum). The amygdalum is a nucleus the shape of an almond situated deep in each temporal lobe. The two nuclei constitute the amygdala and are part of the limbic system, the so-called affective brain, associated with emotionally-based behavior. The amygdala within the limbic system connects to the cerebral cortex, to the thalamus and hypothalamus, and to the brainstem and spinal cord. The amygala is important for the mediation of normal responses to fear-evoking or anxiety-producing stimuli. Epileptic seizures where the abnormal neuronal discharge involves the amygdalum can be manifested by severe sensations of fear and memories of events full of fear. Autonomic changes can accompany this fear with increases in heart rate and blood pressure, dialation of the pupils and pallor. "A majority of the peptides that have been localised with neurons of the brain are found within either neuronal cells bodies or terminals of the amygdala" (Gray). These include cortocotropin-releasing factor (CRF), neurotensin, Enkephalin, Somatostatin and Substance P.
Next we review the systems where neuropeptides are particularly involved.
