The author is especially interested in consciousness - she wrote Journey to the Centers of the Mind: Toward a Science of Consciousness, 1995. She is interested in relations between consciousness, mind and brain… the “neural correlates” of consciousness

In the first three chapters she outlines anatomy, some typical mental functions and cellular structure and function

Chapter 1, Brains Within Brains, looks at the distinct anatomical divisions and concludes that they are not autonomous; rather they are a cohesive system. Asks whether each part has a different function. Concludes that the functions are not localized. Has some general comments on distribution and specificity of function, integration, and neuronal plasticity

Chapter 2, Systems of Systems, approaches the problem of localization of consciousness by looking at mental functions. She concludes again that the functions are not localized

Chapter 3, Pulse, Impulse, takes up the functioning of neural cells and neuro-transmission and neuro-modulation. She also considers the functions of the glial sells. She speculates that the complexity and large number of interconnections, the plasticity of the interconnections - to be taken up in the next chapter, and the variety and variation made possible by neurotransmission and neuro-modulation makes the computational model of the mind improbable

AM: The idea of Francis Crick that the 40Hz oscillations in the visual cortex are associated with visual consciousness is pertinent

The last two chapters consider development, integration of function, and mind-brain relations

In Chapter 4, Cells Upon Cells, she considers development - anatomy, mental function and cell - and considers what light this may shed on mind-brain relations. She reflects on the important topic of consciousness and its biological basis

She considers the question of whether consciousness begins at a specific point of development - conception, birth and so on - or whether the development of consciousness is a continuous process. She argues in favor of the seemingly more natural idea of continuous development - AM: any fixed point such as birth appears to be somewhat arbitrary and the fertilized egg is too simple. It is convenient to distinguish a general low level awareness from “higher” consciousness - clear and discrete, linguistic, self-consciousness. The development may be a continuous and gradual one with periods or bursts of rapid change corresponding the emergence of the higher elements established by the laying down of key brain structures and patterns - including loops - of neurotransmission

Chapter 5 - the final chapter - With Mind in Mind, considers in detail the gross physical and detailed neural structures and processes that are the correlates of memory, various kinds of memory - short and long term memory, explicit and implicit memory and how short term memory over time results over time in laying down of long term memories. The author’s psychological and biological descriptions are simplified

Since memory is “multi-staged and multifaceted” and “captures the individual’s resources for interpreting the world” she considers it to be a hallmark… perhaps the main hallmark of mind

AM: Since processing and memory are dynamically and anatomically integrated in the brain, the choice of memory is a revealing approach to mind and so to mind-brain relations. This relates to the idea that the forms of perception form the bases of the modalities of consciousness and of thought

Although the author cautions that a causal relation between the phenomenological and the physical in the human brain cannot yet be established, “… for the moment, it is sufficient to be aware of the correlation between these two levels… ”

AM: my impression is that she has shown how, in the minute details of function, modern neural science has begun to reveal a meeting ground – the places where mind meets brain

AM: In forming any such conclusion one may recall the processes of growth in other divisions of science that have conceptual content. The empirical - the facts, what is seen - is related to ideas or concepts. The ideas themselves are not seen. Rather they are organizing principles. They suggest new observations. When experiments and concepts are at odds the ideas and the observations come under review and a sufficient weight of disconfirming evidence occasions the reformulation of the concepts and or checking and reviewing the observations. The practical value to this use of concepts is the organizational and predictive efficiency. Further, since the origin of concepts is frequently anthropic in nature, there is also a centering of human being in nature. This in contrast to the view of science as alienating. The middle ground is that certain ways of doing and looking at science and certain uses of science are alienating

AM: Two Problems: Binding and Object Constancy

Note that the essence of this section has been absorbed to Journey in Being / related documents

The integration of memory and processing is the source of an outline to a solution to the binding problem. This is the problem of how the different attributes of an object - visual, tactile… and even the different visual aspects such as color, shape, size… are appear, in perception, as a single object rather than a number of separate sensations corresponding to the different aspects

In some ways this binding problem is a problem because of the one of the ways in which we may look at it: bottom-up in terms of sensations that we identify as components rather than top-down starting with the idea of a whole object. In the history of evolution life always interacted with objects. Still there is a problem because the bottom-up view is one approach to understanding - it is the “atomic” approach often used in science. The idea is reduce a complex object into simple components which can be understood. Build up understanding of the whole based on knowledge of the simple components. This is a key to understanding, to breakdown - psychosis etc. - and to development. I suppose I could get into a whole philosophy here of Holism-Atomism… but I shall not. Suffice it to say that in this example the integral view informs the atomic view

The solution idea is as follows. Initially, in development, a single sensation - a smell - may have no association. As memory is laid down the external stimuli are always of objects - even if extended ones - and so always come in bundles corresponding to objects rather than as isolated sensations. The different attributes are processed and so recorded in memory in different parts of the brain but, since the object is unitary, in association. Upon later encounters with the same object the diverse regions of the brain are stimulated in perception but are bound by prior association. This would be a problem if memory and processing centers were isolated from each other

I think there is a probable affinity between this solution and the form of the solution to the problem of the experience of object constancy. Object constancy is the adjustment of the perceptual [cognitive] system to see an object as having constant attributes such as size, shape, color regardless of the conditions - within limits - of perception such as distance, orientation, and lighting

Undoubtedly other forms of integration - perceptual-conceptual, conceptual-conceptual - are significant in binding… but I will take that up later

Chapter 1 Brains Within Brains

Begins with the experiments of Jean-Pierre-Marie Flourens [early eighteenth century] who found progressive global loss of function rather than selective impairment as he removed more and more of the brains of laboratory animals. He concluded that distinct functions could not be localized

Continues with long discredited phrenology of Franz Gall a doctor born in Vienna in 1758. AM: Why consider long discarded ideas that later became the subject of ridicule? Because [1] they contain hidden assumptions that later more sophisticated theories continued to make… even up to today, [2] despite the parts of older theories that seem obviously ridiculous today they may have contained ideas that, at least in historical context, are interesting and useful. For example, although the measurement of bumps on the skull appear to be totally misconceived, Gall’s list of thirty-two character traits is interesting as history and as insight into the fashion of the era. The traits, supposed to be the building blocks of character, were associated with specific locations in the brain as revealed by the craniology. The ontological assumption is that of essences that form a hierarchy. That Gall’s ideas appear to be so misconceived to us and yet were once the rage somewhere in the borderline between science, fad and fashion can be a lesson for any time

Some main themes of the book

These two approaches set the stage for one of the main themes - localization vs. distribution of function in the brain. AM: The anticipated resolution, that it is a variegated combination of localization and distribution, will also remain inadequate as long as the idea of function is essentialist[1] and static. This latter point is a second though implicit theme

The experiments of Paul Broca [1861] and Carl Wernicke helped discredit phrenology and also show that function is not completely localized - Broca’s and Wernicke’s distinct areas in the brain are two major locations associated with language function

John Hughlings-Jackson [1835-1911], a British neurologist, viewed the brain as organized in a hierarchy… with the higher, most recently developed functions, the human ones, at the top of the hierarchy - in control. The influence of this kind of thinking was seen in psychiatry [superego of Freud] and escape from a higher controlling force in crowd behavior

Next: Paul MacLean’s hierarchical triune brain concept developed in the 1940s and 1950s. The “primitive reptilian brain”, the brain stem, is responsible for instinct; the “old mammalian brain”, the limbic system, responsible for emotion including aggression and sex; and the “new mammalian brain”, the cortex - Latin for “bark”, responsible for rational thought. Does not discredit the triune brain concept. But adds that MacLean’s does not explain how functions are localized

Material on brain size and weight, ration of brain to body weight, differential size of the cerebellum [little brain], differential size of the cortex and its convolutions [surface area. Relations of these factors to intelligence. Does not consider surface area to body size. Development of the cortex related to ability to think. Dolphins are about as intelligent as dogs

Notes on the cortex. About 2mm thick. Divisible, according to different conventions, into functions that belong to fifty to a hundred separate areas - this makes sense up to a point. Some brain areas with “single” function: the motor cortex for conscious motor control; the visual and auditory cortexes for visual and auditory processing respectively; the somatosensory cortex for touch. Multiple and integrated functions: the parietal cortex [top] receives signals from the visual, auditory and somatosensory systems and is involved in a range of motor functions. The function appears to association and coordination of the different sensory modalities and of different motor function; and of sensory with motor function; and more generally with cognitive processes and that includes thought. Hence the alternative names integration or association for the parietal cortex

Interesting Details and Issues

The substantia nigra and is normally black - its cells produce dopamine… and melanin is the end product of dopamine metabolism. In Parkinson’s patients - difficulty walking, stiffness of limbs, hand tremors at rest - the substantia nigra is pink: its cells have died

The target region of the dopamine is primarily the striatum - more on this in the next chapter - that is implicated in movement

But: the same chemical is distributed over many brain regions while each brain region makes and uses many different chemicals. So what is more important when considering brain damage: the brain region concerned or the change in chemical balance in the brain

Another reason that it is difficult to associate functions with particular regions: the neuronal plasticity observed in partial recovery after stroke

Measurement Techniques

X-Ray

CAT-computerized axial tomography

PET- positron emission tomography

MRI- magnetic resonance imaging

MEG-magnetoencephelography

The importance of different techniques

[1] Revealing physiological function: X-Ray reveals altered anatomy; CAT resolution, though based on X-Rays has higher resolution and, through computer imaging, provides 3-D information; PET shows differential and altered metabolism - radioactive glucose or water is inject IV and in the brain positrons emitted collide with electrons and gamma rays emitted form the image; [2] Space and time resolution: MRI measures oxygen concentration but does not require injection - the oxygen alters the magnetic properties of hemoglobin - and can pinpoint areas as small as 1 to 2 mm and measure events over seconds; MEG measures the magnetic field generated by differential electrical activity has superior time resolution but is currently accurate only for the outer regions of the brain

Overall Conclusions for Brain Function

Distributed function and specificity

Neuronal plasticity

Integration

Chapter 2 Systems of Systems

Motion and Sensation in Evolutionary Development of Nervous Systems

Brains are found in multicellular organisms with locomotion -animals… this is the key that makes a “centralized processing” necessary and adaptive. Plants can move in response to light but do not generate moment to moment environmentally aware movements as animals do. Of course environmental awareness requires [is] perception and requires a responsive sensory apparatus and processing

The Reflex Arc Involves Only the Spinal Cord

The reflex arc involves only the spinal cord. However, the normal repertoire of human movement are not fixed responses

Rhythmic, Semireflex Movements Originating in the Brain Stem

Rhythmic movements such as walking and running involve more complex coordination of muscle groups but even these are semiautomatic. The signals for these repetitive movements come the spinal cord and originate in the brain stem. There are four such “motorways” coming down the spinal cord from the brain stem. The first is responsible for semiautomatic and semireflex rhythmic kind of motion just mentioned; a second coordinates movement with visual and sensory information; a third is important for balance and the fourth mediates the motion of individual limbs

Fine Movement Originates in the Motor Cortex

The motor cortex is a strip-like region of the cortex fitting across the brain like a hair-band. Controls motion by signals to the individual digits. Different parts of the body are controlled by different parts of the motor cortex… and the amount of the motor allocated to a given part of the body corresponds to the precision of movement needed. Thus the hands and the lips have an enormous allocation

The motor cortex also exerts a hierarchical influence over the other four movement motorways. And is central in control of movement

Does the Brain Have a Single “Movement Center”?

No, because there are two other “centers”, the basal ganglia and the cerebellum. The cerebellum is important for movements where there is a continuous feedback from the senses which in turn influence the next movement… and could be called the “auto-pilot” of the brain. The basal ganglia, a group of interconnected regions that includes the striatum and the substantia nigra, is associated with “ballistic” movement - motion in a predetermined trajectory. When the striatum is impaired there can be wild involuntary movements [Huntington’s chorea] whereas death of the dopamine producing cells of the substantia nigra results in Parkinson’s disease in which there is difficulty moving at all combined with muscle rigidity and tremor. In normal movement the effects of the striatum and the substantia nigra operate in a balance

There Are Multiple Centers for Movement… that are in Dialog

The cerebellum has strong interconnections with the lateral premotor area that is distinct from and is in front of the motor cortex. The basal ganglia connect to a part of the motor cortex called the supplemental motor area. Damage to the supplemental motor area results in symptoms like those of Parkinson’s disease

The generation of movement is the net result of many brain regions acting together and in interaction

The Somatosensory System… Does it Have a Single Center?

There are two major “motorways” up the spinal cord leading up the spinal cord to the Somatosensory cortex… an area just behind the motor cortex that is responsible for registering touch, temperature… and pain. The first, the evolutionary system, is mainly related to pain and temperature… and the newer system carries precise systems for touch again with disproportionate allocation of cortical regions to hands and lips

May be making the point that there is no single somatosensory center

But sensation has additional, specialized organs for specialized sensation - seeing, hearing, taste, smell… whose inputs to the brain are not passed up the spinal cord

Vision

Considers this in detail. Here I will just note the main points. AM: Vision is the most completely researched of the sensory systems

Compound eye - up to 30,000 facets in some insects. These eyes can be large in relation to body size with more processing in the peripheral organ… than in sophisticated where the input will not already have been heavily biased. The advantages of the compound eye: large visual field, very sensitive to change and to planes of polarization

The human eye - an example of the camera eye - provides high resolution. Light absorbed by cells on the retina and a signal relayed to the optic nerve. The exit of the optic nerve is the blind spot - to the middle of the eye near the nose. Also near the middle but toward the ear is the fovea a small indent densely packed with cones [associated with color vision and perception of fine detail] where the inner layers of the retina are absent, there are no blood vessels, and light has an almost unrestricted passage to the light-sensitive cells. Birds of prey have up to five times more concentrated cells in the fovea than humans. Eagles have two foveas - the search fovea for side vision whereas the pursuit fovea judges depth which is done with both eyes

The human [mammal?] eye can move back and forth in the socket while birds’ eyes are fixed

Two types of photoreceptive cells - rods for vision in low light and cones for color and contrast in normal light. Perception by rods is associated with rhodopsin, which breaks down into retinal and opsin when it absorbs light in the visual range of the electromagnetic spectrum… rhodopsin is continuously regenerated and builds up in the dark. The maximum sensitivity of a completely dark adapted eye is at 5000 angstroms and at this wavelength the threshold for vision is a single quantum and there is a chemical amplification in the rod itself before providing the electrical visual signal from the rod. There are three types of cones corresponding to primary colors: red, green or blue. Other colors are registered by exciting different combinations of the cones in different proportions. The changes that take place in the three cone pigments have not been analyzed, simply because, so far, they have defied isolation, because their concentrations are so much less than that of the rod pigment

The retina does not signal everything in the visual field uniformly. There is an enormous bias toward contrast and motion

Visual Processing

From the retina, cells send signals via the optic nerve to the thalamus - in the diencephalon or middle brain - that relays the signals to the visual cortex

Various integrative functions revealed by different damage to the visual cortex in different individuals. Example: woman in forties with highly localized damage experienced loss of motion perception. Other examples: loss of shape or color or low light perception. Loss of color could be due to damage to the retina or, bilaterally, to critical brain regions; if latter is unilateral half the world appears in black and white and half in color

Agnosia is inability to perceive form… severity varies among patients and for a given patient from time to time… and may be due to hierarchic assembly in perception of complex forms which could be arrested at different stages. Understanding and seeing may be inextricably linked… ”form blindness” may be due [in some cases?] due to loss of integrative processes

Vision of color, form, movement can be independent… with processing in parallel… this raises the binding problem for vision[2] - where and how do the parallel visual signals converge into a single entity. The connectivity and processing responsible for the binding is not centralized but, likely, a balanced dialogue - and staged or hierarchic - among key brain regions

The “Mystery” of Consciousness

“… How do we actually see?” She is asking: AM: How - and where - does the subjectivity, the feeling of awareness itself… how does this arise?… and “the riddle is compounded” by blindsight which apparently involves awareness but not consciousness - in blindsight subjects report not seeing an object but their behavior indicates awareness of it. One idea toward an explanation of this - and of cognitive processing in general - is that the cortex also sends signals to intercept and modify incoming signals from sense organs. Blindsight is perhaps due to rupture in the balanced hierarchic circuitry

… but blindsight also depends on motion: if the object begins to move the subject, in some cases, reports seeing it. In terms of the idea, to be presented later, that processing for different facets of vision[3] - or perception generally - occurs in different brain regions, this makes sense

Prosopagnosia - the failure to recognize faces - is a reverse of blindsight: awareness without recognition. associations can also - idiosyncratically - reverse prosopagnosia

The enigma of consciousness… the first person, subjective conscious element: this is the same as the point above - the mystery of consciousness

A related mystery: why [how] are electrical signals arriving in the cortex experienced as vision, while exactly the same kind of signals arriving in the auditory cortex experienced as hearing? And what of synethsesia… where the distinctions between the senses breakdown - most commonly sound is experienced as color though “virtually any combination of the two plus senses is possible.” Synesthesia may be due to aberrations in the association cortex… or to physiological malfunction at the neuronal level

Arousal and sleep

Level of arousal, as the degree of perceptual intensity of the environment, is a “parameter” of consciousness… and varies from coma to deep sleep to being awake to extreme excitement, fear… One measure of arousal can be monitored as electrical activity averaged over large areas of the cortex

The EEG records activity from cells just beneath the surface of the brain. Scientific application of the EEG is studying electrical activity in the brain and its relation to various mental activities, states and disorders. Clinical application includes diagnosis of disorders such as epilepsy including location of the damaged tissue. Slow waves generated mainly at the back of the head, the alpha waves, correspond to being relaxed and conscious… this is one way to provide “bio-feedback.”

Electrical activity has been recorded as early as the third fetal month but only in the sixth fetal month do slow regular waves emerge. Until age 10 there are two very slow: the theta of 4 - 7 Hz, and the delta of 1 - 4 Hz never seen in healthy awake adults

The EEG reveals four stages of sleep plus rapid eye movement or REM sleep. Humans descend rapidly through stages 1 through 4 after falling asleep… and gradually surface and descend through the four stages throughout the night. REM is dream sleep. In normal sleep one may toss and turn but in dream sleep, when the EEG is the same as when awake, the muscles become paralyzed. In an average night’s sleep of seven and a half hours humans can have two and a half hours of dreams. The longest recorded continuous period of REM is two and a half hours

Reptiles do not display REM, birds do occasionally, all mammals - according to their EEG - appear capable of dreaming

Why do we dream? Is there a value to dreaming? One theory[4] is that, no longer tied down to the reality of the world, the brain begins to freewheel… but it seems to be more than just that since subjects deprived of REM sleep overcompensate on subsequent nights and enter REM more often, and presumably, for a longer total period of time. A second idea is that dreams help adjust to and consolidate recent events. This, too, is probably partial at most since at 26 weeks the fetus spends all its time in REM sleep. REM sleep time gradually decreases during childhood so dreams may be a function of a brain in the process of maturing, of forming connections, when association among brain regions is less

Comments on possible relation to schizophrenia in which waking consciousness is said to be similar to normal - real but illogical - dreaming and brain association is - a possible hypothesis - less

What is the function of normal sleep? Since animals are vulnerable during sleep it must have a benefit. Synthesis in the brain of proteins required for conscious and autonomous brain function is much higher in sleep. Deprived of sleep, energy storage becomes inefficient. Rats deprived of sleep require more food and finally die, underweight and exhausted, despite huge food intake

Brain / body “knows” when sleep is needed. The pineal gland secretes melatonin that is associated with sleep / wake. In humans sleep / wake cycle is controlled in a circadian [bio-]rhythm that is fine tuned by external cues

Pain

… sensitivity to pain also varies over the day. This reminds us that pain is a subjective phenomenon. Nerve conduction apparently does not vary over the day. When arrows were removed from the wounds of injured soldiers, they were often twisted in the wound as are acupuncture needles, and the soldiers sometimes had relief from pain. Similarly acupuncture also relieves pain - sometimes enough to allow surgery. The effect occurs about 20 minutes after insertion of the needles and lasts for about an hour. Applying local anesthetic before applying the needles blocks the analgesic effect of acupuncture - this suggests that transmission or brain reception of pain signals is necessary. The delayed effect suggests that the needles are not directly responsible for the effect of acupuncture but that some natural chemical may be released in the brain. Enkephalin [endorphins], discovered in the early 1970s, are the brains own morphinelike chemical substance. Narcotic antagonists block the effects of narcotics including enkephalin and reduce the effectiveness of acupuncture

Enkephalin are found in a variety of locations in the brain and spinal cord [CNS]

This a particular example of the general point of this chapter that for particular functions - motion, perception… - a number of brain areas are active in parallel. Functions are distributed and the corresponding brain activity is associative

Now begin to look at brain-mind in a “bottom-up” approach… at the cell level where the details of the signal and memory processes lie… so as to understand, in detail, the underlying mechanisms

Chapter 3 Pulse, Impulse

A typical body [non-neural] cell is 20 - 100 m m in dia

Electrical [nerve] signals are transmitted at some 220 miles per hour

Early experiments: Golgi Stain

Camillo Golgi 1843 - 1926, a medical graduate of Padua University discovered that silver nitrate stains one in ten to a hundred neurons black… and so the stained neurons appear black on a pale background

The soma or body of a neuron comes in a variety of shapes: round, oval, triangular, fusiform - spindle like… Like other cells, the soma contains the “life support” organs for the neuron

The neuron has many dendrites or branches - that receive electrical signals from other cells, a soma and an axon, a long fiber that transmits signals when fired by the cell, many times longer than the rest of the neuron - up to a meter in the spinal cord. Relative to the thin axon, hard to see even under a microscope, the dendrites are short and stubby. According to the density of the dendrites there appearance of neurons varies enormously - there are at least 50 basic shapes

Incoming signals are not transmitted directly - individually or in combination. If some combination of incoming signals is strong enough the neuron is “triggered” and generates a signal

Channels and Action Potentials

Luigi Galvani 1737 - 1798 showed nerves from the spinal cord generate electricity and thought all electricity lay in living tissue… but Michael Faraday 1791 - 1867 showed the fundamental and universal nature of electricity

In neurons flow of electricity is due to one of four ions potassium on the inside and sodium, calcium, or chloride on the outside. The membrane of a neuron has two layers with a non-conducting fatty middle that prevents ions from moving in or out. There also negatively charged proteins inside the cell and normally the inside of the neuron is -70 to -80 mV relative to the outside. This state of disequilibrium is maintained by the sodium-potassium pump

The membrane barrier can breached through protein pathways or “channels” across the membrane… these conduct the ions

The Action Potential of 1 - 2 ms

As a consequence of the trigger described above the following occurs:

Depolarization: Sodium ions [Na⁺] briefly enter the cell through sodium channels making the potential +20 mV relative to the outside

Hyper-polarization: K⁺ ions leave the cell resulting in overshoot of the normal -70 to -80 mV in which the inside potential becomes -90 mV

The transient positive-negative wave is the action potential

Re-polarization: K⁺ ions leave through potassium channels

The actual process is more complex involving a calcium channel, hypothesized anion [Cl^-] for which there is some evidence

Output reflects “net input” not through intensity [-90 mV] but by frequency of the action potentials. 1 - 2 Hz is slow, 30 - 100 Hz is normal, and some neurons achieve 500 Hz

Francis Crick thinks that the 40 Hz oscillations in the visual cortex and elsewhere are associated with consciousness primarily because this frequency is associated with binding

Neuron to neuron transmission - the Synaptic Gap

Golgi thought neurons were joined together somewhat like a hair net… but was opposed by the Spanish anatomist Ramon y Cajal who held that there was a gap between neurons

Experimental study became possible with the advent of the electron microscope capable of x 10,000 - the first true electron microscope was built in 1933 but it was a while before the x1,500 magnification of the light microscope was surpassed and the problem of heating and destruction of specimens was solved

In the 1950s the electron microscope showed Cajal was right. However, it turns out that while transmission across a synaptic gap is the primary mode some neurons are fused at “gap junctions” where transmission is more rapid and requires less energy

One objective of the next topic is to see what advantage neurotransmission across a synaptic gap may have over the faster and more efficient - with respect to time and energy - gap junction process

Neurotransmission and neurotransmitters

In the 19^th Claud Barnard, a Frenchman, suggested curare works by interfering with transmission of nerve signals. Beginning early in the 20^th century it was shown that curare works by blocking the neurotransmitter acetylcholine or ACH

Neurotransmitters - are released from nerves and neurons in the brain. AM: Some neurotransmitters are acetylcholine - the first chemical occurring in the nervous system shown to be a neurotransmitter, epinephrine and norepinephrine, dopamine, serotonin [5-hydroxytryptamine]. It is, apparently, hard to show that a chemical found in the brain is - or is not - in fact a neurotransmitter. The following are some probable neurotransmitter [neuromodulator] amino acids - excitatory such as glutamic acid and aspartic acid and inhibitory such as gamma-aminobutyric acid [GABA] and glycine, histamine, adenosine triphosphate and neuroactive peptides. There is evidence that the stated amino acids act as excitatory or inhibitory neurotransmitters. The neuroactive peptides are sequences of amino acids usually longer than amino acid transmitters but shorter than proteins and hormones and are different from the classic neurotransmitters in a number of ways including synthesis, duration of action - several seconds to days in contrast to milliseconds for, e.g., acetylcholine. The peptides are associated with neuromodulation. This is scratching on the surface with respect to mechanisms and modes of action and detail of a system of information that is in flux

ACH is stored in vesicles at the end of the axon. The number of vesicles emptying their contents is proportional to the number of action potentials… and in this way the electrical signal is converted into a chemical one… the synaptic gap is crossed with thousandths of a second or milliseconds = 0.001s. At the outside of a dendrite of a receptor neuron the transmitter binds to a matching protein called a receptor and the combined complex molecule triggers the opening of a channel and so sets up a transient potential difference that is one of many signals transmitted down the dendrites to the body of the cell… and the cycle is set to repeat

Once the transmission is done the transmitters must be removed and the vesicles replenished… and this takes additional energy

What are the advantages of chemical transmission? There are 10¹¹ neurons in the human brain each with ten to a hundred thousand neurons connecting to it. Transmission with neurotransmitters adds versatility. The input to a neuron is summed over the 10 to 100 thousand inputs of varying intensity; neurotransmission adds to this complexity by having many different neurotransmitters each with its own target and different effect on the final voltage; this is further enhanced by modulation. The variety and amounts of the neurotransmitters released depends on the different inputs and their degrees of activity. Additionally, due to the interaction between the limbic system and the endocrine / hormonal / neurotransmitter system this points to a mechanism for an effect of emotion and mood upon cognition and thought

Drugs

Nicotine docks at one type of ACH receptor and so mimics the action of ACH. Alteration of neurotransmission is the basis of action of many nervous system drugs including those that alter mental states and processes. In addictive drugs the normal action of neurotransmission is severely altered and thus the basis of use and, at the same time by de-sensitization, of physiological habituation and add