Notes to Neuroscience For Dummies

Published by: John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030-5774, www.wiley.com Copyright © 2023 by John Wiley & Sons, Inc., Hoboken, New Jersey

The human brain consumes about 20 percent of the body’s metabolism despite being only about 5 percent of body weight.

Humans are now beginning to augment ourselves.

Most of the volume of the brain is axonal wiring, not cells.

the corpus callosum, which contains 200 million fibers.

This “motor map” (called a homunculus)

Primates, on the other hand, have complex male and female hierarchies and may hatch plots against each other that span years of planning.

The major sensory inputs from the skin (touch, temperature, and pain receptors) relay through the thalamus to the gyrus just posterior to the central fissure, where a map of the skin exists.

The skin homunculus map closely resembles the primary motor cortex map.

The fact that the visual system gets an entire lobe for processing emphasizes the importance of high visual acuity and processing among our senses.

The root of the word thalamus comes from a Greek word (tholos) related to the entrance room to a building, so you can think of the thalamus as the gateway to the cortex.

So, what does the thalamus do, exactly? It functions like a command center that controls what information goes between different parts of the neocortex and the rest of the brain.

Memory modifies behavior in such animals via what we think of as emotions.

one brain structure within this system, the hippocampus, is now known to have a crucial function in the creation of memory.

primarily involved with emotional processing, the amygdala.

the basal ganglia. The basal ganglia consist of five major nuclei: the caudate, putamen, globus palladus, substantia nigra, and subthalamic nucleus

Parkinson’s disease, which is caused by the death of dopaminergic neurons in this nucleus. Without these neurons, initiating voluntary movement or changing an ongoing movement sequence becomes difficult.

The major visual area in the midbrain is the superior colliculus, which controls eye movements called saccades.

(called the tectum in frogs and other non-mammals)

The reticular formation is not so much a defined structure as it is a continuous network that extends through and interacts with numerous brain areas.

trigeminal cranial nerve V.

cytoplasm

dendrites receive inputs

axon sends the output of the cell to other cells.

learning. Learning occurs when experiences modify the strength and identity of the interconnections between neurons and thus create memory.

electrical pulses, called spikes,

synaptic cleft.

Motor neurons output their neurotransmitter (acetylcholine) onto muscle cells that contract when receptors in the muscle cells receive it. The control of voluntary striated muscle generally occurs after the brain has done a

Postsynaptic receptor channels that are activated by neurotransmitters released by a presynaptic neuron are generally referred to as ligand-gated ion channels.

neurotransmitter molecules.

All voluntary muscle contractions are caused by the release of acetylcholine by motor neurons onto muscle cells.

fast inhibitory neurotransmitters gamma amino butyric acid (GABA)

Slow neuromodulators that include both excitatory and inhibitory types: Most of the fast neurotransmitters are amino acids (other than acetylcholine). Modulating neurotransmitters include biogenic amines, such as the catecholamines (dopamine,

cation is positively charged (attracted to a negative cathode); an anion is negatively charged (attracted to a positive anode).

astrocyte

cancer treatment protocols effectively involve using toxic chemicals and radiation to wipe out the vast majority of dividing cancer cells, hoping the immune system can mop up the last few percent.

because some neural projections from the face invade the cortical area once stimulated by the limb and cause sensations to be perceived as being located in the limb, even when the limb is gone. Receptor densities

endorphins (a term which is an abbreviation of endogenous morphines).

it turns out that the drug naloxone not only reduces the effects of opioids, such as heroin, but it also reduces the placebo effect. What this means is that the placebo effect isn’t just psychological; it actually has a physiological component, involving the cognitive stimulation, from belief, of the body’s internal endorphin production that objectively and measurably reduces pain by binding the endorphin receptors.

(red, green, and blue).

apraxis, the inability to skillfully execute tasks requiring visual guidance.

Unlike the preceding retinopathies, glaucoma involves a primary death of retinal ganglion cells, most commonly due to inherited excessive pressure within the eye. One glaucoma subtype, closed-angle glaucoma, is treatable with laser surgery. The other form, open-angle glaucoma, can often be controlled with medication.

Amblyopia,

they also are apparently derived evolutionarily from motor type cilia, such as used by some single-celled organisms to move.

of attended auditory input

deliberately try to hear—is mediated in multiple brain areas that

22 results in an inability to process prosody in language—the changes in tonality and rhythm—that conveys meaning. Patients with this damage, for example, have trouble distinguishing sarcastic versus questioning versus other tones of voice, and in particular, don’t “get” jokes and other forms of humor.

However, its processing relies more on the right than the left side of the brain, indicated by the fact that most people recognize melodies better with their left ear (right brain).

age-related decline in high frequency sensitivity (presbycusis, which occurs in almost everyone, particularly males),

This pathway is concerned with memory associations of very universal smells such as something rotting, rather than sophisticated smells such as hazelnut coffee and dark chocolate, which require higher order cortical processing to establish their identity prior to being stored in memory.

trigeminal

alliesthesia (“ changed taste”), and it’s a brain mechanism that indicates you’re getting full. The mechanism for

Proprioception

kinesthesis

Some researchers have argued that language itself, the ultimate separator of humans from animals, evolved literally hand in hand with manual dexterity. This argument suggests that the left side of the brain regions that enable language production also makes most of us right-handed for motion sequence production.

cells. The nicotinic acetylcholine receptor is an excitatory ionotropic receptor (refer to Chapter 3).

cholinesterases)

myosin myofilaments

ATP (adenosine triphosphate) as an energy source. ATP is the universal energy “currency” within cells for conducting

Myasthenia gravis

Motor neuron viral diseases: Rabies and polio

One focus is based on the fact that the myelin wrapping around peripheral nerves is from cells called Schwann cells, but the myelin wrapping around central nervous system axons is from cells called oligodendrocytes.

The beginning of the withdrawal reflex can also be described as being ballistic, in the sense that once launched, its trajectory is not controlled

Patients with tremor, such as Parkinson’s, have defective overshoot control systems so their limbs oscillate at what should have been the endpoint of a planned movement.

The basics of locomotion

central

pattern generator, which alternates the two legs and two arms with each

So the question is, how does repetition make us better at doing something?

Does consciousness emerge from just having a large enough brain? Or is consciousness not real, not a cause of anything, but a result, an illusion that goes along for the ride with complex brain activity, what some philosophers call an epiphenomenon? This chapter considers some of the more relevant data.

an orderly map, referred to as the motor homunculus (this is very similar to the sensory homunculus in the primary somatosensory area;

items that humans can hold in memory (which memory researchers call chunks)

Selection: How the basal ganglia function as a circuit is one of the least understood areas of system neuroscience, despite their importance in diseases such as Parkinson’s

the basal ganglia structures called the caudate and putamen, which together are referred to as the striatum. The striatum projects to three interconnected nuclei within the core of the basal ganglia, called the globus pallidus, subthalamic nucleus, and substantia nigra (in the midbrain). The output of these three nuclei, particularly the globus pallidus, inhibits motor areas through the thalamus.

our apparent multitasking is really a case of cyclic time sharing.

Here’s what the data very reliably showed: Deflections of the EEG traces occurred typically one-half second before the subjects indicated they’d decided to move their hands (this deflection is typically now called a readiness potential,

abnormalities in the frontal lobe, particularly the orbitofrontal cortex, seem to reduce a person’s capacity to make wise choices without reducing the capacity to do the mental calculation of the costs and benefits of the choices.

Mirror neurons are visual neurons that fire not only when an animal, such as a monkey, is performing a task requiring visual feedback, but also when the monkey observes a human (or presumably another monkey) performing the same task.

L-dopa treatments eventually cease working because the cells that convert L-dopa to dopamine cease working or die.

deep brain stimulation (DBS).

homeostasis, the active maintenance of various aspects of the internal state of our bodies.

The autonomic nervous system is actually a dual system because it has two components, called the sympathetic and parasympathetic branches, which act in opposition to each other.

suprachiasmatic nucleus (SCN), which means “nucleus above the chiasm.” Although the activity of these cells controls the overall circadian rhythm in humans and all other vertebrates, circadian cells also exist in primitive organisms and circadian rhythms exist in single-celled entities such as algae.

learning and its result, memory.

Researchers conjecture that memory for navigation may have been the original evolutionary function of

the hippocampus, after which it became involved in other kinds of memory, including particularly episodic memory

Stroop task,

(the “singularity”) should be reached around 2030,

consciousness as “the remembered present.”

few of us remember anything from our lives before the age of 2 is suggested to result from the profound reorganization of our brains that occurs after we learn language,

whether it enables complex functions like language and consciousness simply because it has crossed some size threshold, or whether its structure and organization is somehow unique.

The small “communities” in the cortex are called minicolumns.

passing through six synapses or less, the six degrees of separation.

Past stimuli have left their trace in memory not only as recallable objects and events, but also as paths in the brain through which current stimuli are processed. Stimuli received by the senses are transformed into a universal neural currency of action potentials bombarding the thalamus.

areas is a central executive processing nucleus within the thalamus itself called the pulvinar.

Remembering involves activation of many of the same brain structures (visual, auditory, and somatosensory cortices) that processed the original sensory input, organized or activated by the hippocampus,

and represented in the firing of working memory neurons in the lateral prefrontal cortex.

Beyond this basic crossed-innervation scheme, the two sides appear to have different styles of processing that are particularly evident in some high-level cognitive tasks. These include a left-side specialization for grammatical aspects of language and a right side specialization for holistic aspects of visuo-spatial processing.

In virtually all right-handers and about half of left-handers, language depends far more on structures in the left hemisphere than the right (the homologous areas in the right hemisphere have far weaker roles in the same functions).

stylistic

manners of processing by the two hemispheres: The left brain tends to be sequential and rule-based, whereas the right brain tends to do pattern matching.

Wernicke’s area and Broca’s area.

If you heard Wernicke’s aphasics speak in a language you did not know, you might have difficulty discerning that there was anything wrong.

The right fusiform face area, a very anterior and medial part of the visual identity processing stream in the infero-temporal cortex, is more important for face recognition than the equivalent area on the left.

According to this idea, humans are unique in that we have a system in the sequential, rule-based left side of the brain that constantly tries to make sense of the world by using language. This left side interpreter is constantly making up a verbal story about reality that includes salient events and the role of the person and their actions in those events.

Does a car simulate a person walking?

Evolution has occurred in the mammalian brain mostly by adding the neocortex to ancestral structures. This is something like the addition of numerous microcomputers and controllers to a modern car engine.

Despite the fact that humans have much larger brains than many other animals, the capacity of seven short-term memory items doesn’t appear to be much greater than that of many other animals, such as crows!

Lateral prefrontal damage is associated with a phenomenon called perseveration.

Wise people with intact frontal lobes make this change in priorities; teenagers with not yet fully developed frontal lobe myelination, and people with compromised frontal lobe function, often do not.

On the other hand, intuition can lead to stereotypes and rigidity in behavior.

The orbitofrontal cortex informs us when we contemplate socially

embarrassing actions by provoking feelings of fear and embarrassment through the action of the autonomic nervous system.

practiced sequences to be executed with higher precision and speed than is possible under explicit conscious control. Because such sequences

are executed faster than they can be consciously controlled, they are executed with only high level awareness of their progress, without knowledge of the motor details.

(called voxels)

The anterior cingulate is activated when you do things that are difficult or novel, when you make errors, or when you must overcome habitual behavior patterns. It is at the center of a supervisory control system that mediates goal selection

In normal human development, the frontal lobes mature last. For example, myelination of axons is not complete in the frontal lobes until late adolescence.

Adolescence is a developmental period notoriously characterized by high raw intelligence but poor judgment typical of inadequate frontal lobe function. One of the oft-stated goals of education is to instill enough good habits and rational thinking capabilities to get adolescents through adolescence without doing harm to themselves or others.

During embryonic growth and the first years of life, the human brain develops by growing and changing its large-scale organization. Starting during early development but continuing throughout later life, nervous system activity from experience causes changes in synaptic strengths that mediate changes in behavior.

at least three kinds of adaptation to the environment are possible: evolutionary adaptation, developmental adaptation, and classical learning.

A crucial brain area for consolidating learning from short-to long-term memory is the hippocampus in the medial temporal lobe.

There are two low-order mechanisms by which neural responses change: adaptation (or habituation in the case of repeated stimuli) and facilitation (sensitization in the case of repeated stimuli):

neural circuits also appear to operate like analog computers, so the brain is a mixture of both).

How does a synapse change its strength? What and where are these synapses?

What signal controls this change that is associated with learning?

glutamate. However, unlike most ligand-(neurotransmitter-binding) activated receptors, the NMDA receptor is blocked by a magnesium ion in the mouth of the pore when the neuron is at its normal resting potential with the inside about–56 millivolts with respect to the outside extracellular fluid. In this case, binding glutamate from a presynaptic terminal is not sufficient to open the NMDA ion channel. The magnesium ion is removed, however, if an adjacent non-NMDA glutamate ion channel (typically those called AMPA and kainate channels) is also activated and depolarizes the neural

called long-term potentiation. (There is also long-term depression, which balances things out so that all synapses do not become stronger only.)

Cognitive neuroscience seeks to locate where in the brain these memories exist and what processes they use. The hippocampus, as it turns out, is crucial for moving memory from the short-term form to the long-term.

Short-term memory exists in two places, the lateral prefrontal cortex and the hippocampus.

coincidence detector for that thing. So seeing a green frog activates the cortical areas for green and frog, which activates the hippocampal green frog cell whose synapses get strengthened.

This means you can re-create in your cortex a version of the pattern of activity that occurred when you actually experienced something.

When you continue to think about, or rehearse, the memory of some experience, the activity reverberates between hippocampus and cortex. If you rehearse enough (which happens during REM sleep, particularly), modifiable synapses in the cortex are changed so that the cortex itself can reproduce the neural activity associated with an experience.

The hippocampus is a scratchpad for maintaining rehearsal to form the long-term memory.

their hippocampi played back the correct maze traversal sequence by activating, in sequence,

playback occurred at about seven times the actual speed that the rats ran the mazes. If the rats were prevented from having REM sleep, they did not consolidate the day’s training well and did not learn the mazes as well.

The name for contextual memory is episodic memory, that is, memory associated with an event or episode. General memory about facts is called semantic memory.

Remember also that the projections from neocortex to hippocampus include both low (realistic, detailed) and high

(abstract) meaning associated levels, so that the context for any memory can be quite elaborate and specific.

too weak (the synapses are not sufficiently strengthened)

scuba divers who learned a list of words underwater and then were asked to recall the terms later, both on the surface and underwater. The results? The underwater performance was better.

soap opera syndrome of temporary memory loss, known clinically as transient global amnesia (TGA).

transient ischemia,

Learning has a lifespan trajectory. It’s easy when you’re very young, difficult after adolescence, and very hard for most elderly. We can’t do much about the process of aging other than taking care of ourselves, but we can maintain and even increase the ability to learn by engaging in intellectually challenging activities.

Cognitive dysfunctions such as dyslexia and dysgraphia are not believed by most scientists to be based on any specific dysfunction in learning mechanisms. Rather, they are almost certainly the result of a dysfunction in some aspect of the central representation of the relevant sensory input that becomes evident during learning.

enough time for the hippocampal-cortex reverberation system to consolidate learning over several evenings of sleep.

Failure is a signal to change synaptic weights, while success means that some subset should be enhanced.

One of the functions of the dopamine system in the brain is to provide reward/ punishment feedback for adapting the brain to activities in which you are engaged.

glial

genome codes for rules by which several hundred brain areas will come into existence. A few other rules specify the approximate location of these areas, about how large they are, and about what kinds of connections they will have. This constitutes a general program for development.

This developmental fine tuning is called plasticity.

cell type, such as a pyramidal cell. This migrating cell is called a migratory precursor cell.

are pluripotent stem cells, meaning that they can differentiate into any cell type. As development proceeds, they become committed to being endoderm, mesoderm, or ectoderm cell types, then to specialized types within those divisions, and so on, until they differentiate into a final cell type and remain so for the life of the organism, never dividing again (with a few exceptions).

Some researchers believe that subtle errors in laying out these standard minicolumns properly may underlie some disorders such as autism.

A major question in neuroscience concerns how axons know where to go and what to connect to when they reach their target areas.

What the genetic code really codes for is a set of cellular responses that comprise rules or procedures that cells follow when responding to their environments, which they do through the manufacture of proteins.

Tests have shown that at birth, infants are already familiar with their mother’s voice from hearing it in the womb, for example. This is possible because neurons in newborns’ auditory cortices already respond better to the speech sounds of their mother in her language than to other voices in that language or to the mother speaking a different language she did not use while they were in the womb.

RNA contains the sugar ribose instead of the deoxyribose in DNA. The complementary base to adenine in RNA is uracil rather than the thymine in DNA. RNA is single stranded while DNA is double stranded.

Another process, called reverse transcription, uses RNA from a virus that has entered the cell to make DNA in the cell nucleus. Reverse transcription occurs in retroviruses such as HIV and is a common feature of the replication cycle for many viruses by which they hijack the cell’s transcription machinery to make copies of themselves.

The first part of the experiment is whether this new genome can control the development of a viable fetus that will progress to full term and birth.

genotype)

phenotype).

elucidation of the CRISPR-Cas9

degeneracy.

the developing embryo. The general term for substances that cause birth defects is teratogen.

axon myelination,

continues until nearly the end of adolescence.

telomeres at the end of chromosomes inside the nucleus of cells may only be capable of a finite number of divisions. Each time a cell divides,

At the whole organism level, joints wear out and blood vessels harden or get clogged with deposits.

accumulation of more or less random degeneration in multiple tissues

telomere shortening

In cognition, the accumulation of knowledge and experience tend to compensate in later years for slightly slower reactions and short-term memory capacity.

Fluid intelligence

Crystallized intelligence

tennis, which seems to have benefits over and above simpler kinds of exercise, such as jogging.

choline

nootropics)

Aging is a major risk factor for many neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, and vascular disease that affects the brain,

The neurons that die in the initial stages of Alzheimer’s disease are primarily cholinergic (they use acetylcholine as a neurotransmitter),

Parkinson’s disease is associated with death of dopaminergic cells in a specific basal ganglia nucleus called the substantia nigra (which is actually in the midbrain). The death of these cells interferes with the patient’s ability to make voluntary movements or voluntary corrections during walking, such as stepping over an obstacle.

Researchers have had difficulty telling whether this disease is due to a genetic deficiency that simply takes a long time to play out or a combination of a genetic susceptibility plus an environmental trigger.

(MPTP)

Ischemic strokes in which vessel blockages produce loss of nutrient and waste transport. Hemorrhagic strokes in which blood vessels leak blood into the brain.

psychology

psychiatry

The main reason for this division is the former’s fundamental belief in the causality of mental states.

therapy is used to assess the effectiveness and progress of the pharmacological treatment rather than as the primary treatment tool itself. The most sophisticated approaches may use pharmacological therapy to potentiate cognitive or behavioral therapy.

Traumatic events cause an overactive adrenaline response, which persists after the event, making an individual hyper-responsive to future fearful situations.

Most anti-depressants (particularly recent ones like Prozac) are designed to elevate serotonin levels; many also tend to elevate the levels of norepinephrine and dopamine.

DBS stimulation of the subthalamic nucleus has produced immediate symptom relief in thousands of such Parkinson’s patients (the subthalamic nucleus is part of the neural circuit in the basal ganglia that also includes the substantia nigra, the brain areas primarily affected by Parkinson’s disease).

retrograde

anterograde

GABA transmission (GABA is the most important and ubiquitous fast inhibitory neurotransmitter in the brain).

some internal source in the brain is generating activity in auditory areas that the schizophrenic cannot distinguish from actual hearing.

anhedonia

Obsessive compulsive disorder (OCD) is an anxiety disorder characterized by intrusive thoughts that lead to repetitive behaviors in order to alleviate the anxiety related to the thought.

OCD has been linked to an abnormality in the serotonin neurotransmitter system and is sometimes successfully treated with SSRIs (selective serotonin reuptake inhibitors).

typical antipsychotic

atypical antipsychotic

medications,

(GABA is the key inhibitory neurotransmitter in the brain).

serotonin enhancers

Attempts to supply dopamine to make up for its loss in the substantia nigra, as in Parkinson’s disease, failed because dopamine does not cross the blood–brain barrier if administered into the blood stream. However, its precursor in the pathway for its synthesis in cells, L-dopa, does. L-dopa injections can mitigate Parkinson’s symptoms for several years but eventually becomes ineffective.

dyskinesias.

Cannabinoids found in marijuana activate receptors called CB1 and CB2 that are involved in the brain’s pain and immune control systems.

Thalamus,

The function of the cerebellum is to modulate and coordinate motor behavior.

process has become programmed within your cerebellum and its connections to motor cortex.

The hippocampus can play back a sequence of events in context and activate the cortical areas that were activated by the event itself. This playback occurs typically during sleep, especially during REM sleep. The result of the playback is that the memories that were stored for a short term in the hippocampus cause long-term storage back in the neocortical areas that were activated during the original episode.

area on the right side of the brain corresponding to Wernicke’s on the left processes tone of voice indicating irony, humor, and other aspects of what is called prosody.

The fusiform face area (FFA) is a region of the medial temporal lobe that underlies our learned ability to recognize faces or even, in some cases, discriminate models of cars or species of birds that are similar in appearance.

salient

The main brain area responsible for working memory is the lateral prefrontal cortex.

The basal ganglia are a complex, interconnected set of subcortical nuclei that control behavior at the level below the neocortex. The substantia nigra performs a crucial modulatory role in this system. One reason that the basal ganglia have become relatively well known is Parkinson’s disease, which is caused by a degeneration of dopamine producing neurons in the substantia nigra.

you can think of the lateral prefrontal cortex as holding the content of thought and the ACC as selecting that content.

Neurons are cells.

This specialization evolved because it allowed organisms to increase their survival chances by moving within their environment based on sensing things like food, toxins, temperature, and predators.

Neurons receive information via synapses.

Synapses are either electrical or chemical.

cause action potentials

When ion channels are open and allow sodium ions to flow through, the neuron is excited. It is inhibited when potassium or chloride channels are open.

electrophysiologists

The effort to uncover principles of learning and memory used to be called the search for the engram, the memory trace in the brain that constituted a memory.

Learning in the hippocampus is unique because it consists first of changes in synaptic strength, followed by growth of new neural connections, and then new neurons.

Retroviruses can be engineered with sequences that knock out host genes or insert new genes into the host.

how to grow a larger human neocortex in the next few years.

Neural stem cells transplanted into a brain area where the patient’s own cells have died, such as the Subtantia Nigra in Parkinson’s disease, may produce replacement cells as the stem cells sense their local environment and differentiate into the needed neural types.

Some Parkinson’s patients, for example, can be seen to exhibit the typical stooped posture and shuffling gate with the device off, but, as soon as the current is turned on, they are able to walk and engage in sports like basketball.

Experiments have demonstrated that humans (and monkeys) can use electrode arrays implanted in their motor cortices to move computer cursors and artificial arms just by thinking about doing

the techniques for brain-computer interfacing are already here, already being used, and rapidly improving.

Highly proficient computer tutors are being embodied in avatars, computer simulations of teaching characters with whom the student interacts.

Nanotechnology

afferent:

ageusia:

amygdala:

limbic

apraxia:

associative memory:

The ability to remember a relationship between two different things, usually by modifying synapses so that particular neurons fire to the constellation of associated items.

basal ganglia: A set of subcortical nuclei that control movement sequences via their output to the thalamus.

biogenic amines:

catecholamines

central pattern generator:

descriptive term for the neural organization within the spinal cord that coordinates four-or two-limbed movement without the necessity for cortical input.

notochord.

codon:

Cortisol is the primary stress hormone

dopamine: A

biogenic amine neurotransmitter.

efferent:

glial

hippocampus: A limbic system structure involved in converting short-term memories to long-term memories.

macular degeneration:

metabotropic (receptor):

myelin:

Almost all neural regions in the occipital lobe are involved in vision.

temporal lobe

somatic

autonomic

enteric

pinna:

postsynaptic: The receiving side of a synapse,

presbycusis: The decline in hearing sensitivity as a function of age,

presynaptic:

nucleic acid

protein.

semantic memory:

serotonin: A biogenic amine neurotransmitter.

episodic memory.

spinocerebellar tract:

substantia nigra:

temporal lobe: The area of the neocortex on each side of the brain.

trigeminal nerve: The cranial nerve V that sends touch, temperature, and pain information from the face to the brain. It consists of three divisions: ophthalmic, maxillary, and mandibular.