Chapter 4- Anatomy Of The Nervous System Flashcards
The anatomy of the nervous system
Neuroanatomy
What are the two main divisions of the vertebrate nervous systems called?
The central nervous system CNS and the peripheral nervous system PNS
The brain and the spinal cord
Central nervous system CNS
Nerves outside the brain and spinal cord
Peripheral nervous system PNS
Part of the PNS that consists of the axons conveying messages from the sense organs to the CNS and from the CNS to the muscles
Somatic nervous system
Part of the PNS that controls the heart, intestines, and other organs
Autonomic nervous system
Located toward the back
Dorsal
Toward the stomach
Ventral
In four-legged animals, The top of the brain is dorsal or on the same side as the animals back, and the bottom of the brain is ventral or on the stomach side. The same would be true for you if you got down on your knees and crawled
The dorsal-ventral axis of the human brain is at a right angle to the dorsal-ventral axis of the spinal cord
Toward the front end
Anterior
Toward the rear end
Posterior
Above another part
Superior
Below another part
Inferior
Toward the side, away from the midline
Lateral
Toward the midline, away from the side
Medial
Located close or approximate to the point of origin or attachment
Proximal
Located more distant from the point of origin or attachment
Distal
On the same side of the body. For example, two parts on the left or two on the right
Ipsilateral
On the opposite side of the body. For example, one on the left and one on the right
Contralateral
A plane that shows brain structures as seen from the front
Coronal plane or frontal plane
A plane that shows brain structures as seen from the side
Sagittal plane
A plane that shows brain structures as seen from above
Horizontal plane or transverse plane
What does dorsal mean, and what is its opposite?
Dorsal means toward the back, away from the stomach side. It’s opposite is ventral
What term means toward the side, away from the midline, and what is its opposite?
Lateral; medial
If two structures are both on the left side of the body, they are ______ to each other. If one is on the left and the other is on the right, they are ______ to each other
Ipsilateral; contralateral
A row or layer of cell bodies separated from other cell bodies by a layer of axons and dendrites
Lamina
A set of cells perpendicular to the surface of the cortex, with similar properties
Column
A set of axons within the CNS, also known as a projection. If axons extend from cell bodies in structure A to synapses onto B, we say that the fibres “project” from A onto B
Tract
A set of axons in the periphery, either from the CNS to a muscle or gland or from a sensory organ to the CNS
Nerves
A cluster of neuron cell bodies within the CNS
Nucleus
A cluster of neuron cell bodies, usually outside the CNS, as in the sympathetic nervous system
Ganglion
A protuberance on the surface of the brain
Gyrus
A fold or groove that separates one gyrus from another
Sulcus
A long, deep sulcus
Fissure
The bulges in the cerebral cortex are called ______. The grooves between them are called _______.
Gyrus; sulcus
Part of the CNS; it communicates with all the sense organs and muscles except those of the head. It is a segmented structure, and each segment has on each side a sensory nerve and a motor nerve.
Spinal cord
The concept that the entering dorsal roots carry sensory information and the exiting ventral roots carry motor information
Bell-Magendie law
Clusters of sensory neurons outside the spinal cord
Dorsal root ganglia
Areas of the nervous system that are densely packed with cell bodies and dendrites
Gray matter
Area of the nervous system consisting mostly of myelinated axons
White matter
In a cross-section through the spinal cord, the H-shaped _____ ______ in the centre of the cord is densely packed with cell bodies and dendrites. The ______ ______ consists mostly of myelinated axon’s
Gray matter; white matter
A network of nerves that prepare the organs for vigourous activity
Sympathetic nervous system
System of nerves that facilitate vegetative, non-emergency responses by the body’s organs
Parasympathetic nervous system
The autonomic nervous system consists of neurons that receive information from and send commands to the heart, intestines, and other organs. What are the two parts of the autonomic nervous system?
Sympathetic nervous system; parasympathetic nervous system
Describe the functions, locations, and organization of the sympathetic nervous system
Prepares the organs for vigourous activity
Consists of chains of ganglia just to the left and right of the spinal cord’s central regions (The thoracic and lumbar areas). These ganglia are connected by axons to the spinal cord.
Sympathetic axons prepare the organs for “fight or flight” – increasing breathing and heart rate and decreasing digestive activity.
Because the sympathetic a ganglia are closely linked, they often act as a single system “in sympathy” with one another.
The sweat glands, the adrenal gland’s, the muscles that constrict blood vessels, and the muscles that erect the hairs of the skin have only sympathetic, not parasympathetic, input
Most of the postganglionic synapses of the sympathetic nervous system use norepinephrine, although a few, such as those that control the sweat glands, use acetylcholine
Describe the functions, locations, and organization of the parasympathetic nervous system
Facilitates vegetative, non-emergency responses. The term para means “beside” or “related to”, and parasympathetic activities are related to, and generally the opposite of, sympathetic activities
Parasympathetic activity decreases heart rate, increases digestive rate, and in general, conserves energy
Also known as the craniosacral system because it consists of the cranial nerves and nerves from the sacral spinal cord. Unlike the ganglia in the sympathetic system, the parasympathetic ganglia are not arranged in a chain near the spinal cord. Long preganglionic axons extend from the spinal cord to parasympathetic ganglia close to each internal organ. Shorter postganglionic fibres then extend from the parasympathetic ganglia into the organs themselves.
Because the parasympathetic ganglia are not linked to one another, they act more independently then the sympathetic ganglia do.
The parasympathetic nervous system’s postganglionic axons release the neurotransmitter acetylcholine.
Because the two systems, the parasympathetic and sympathetic nervous system’s use different transmitters, certain drugs excite or inhibit one system or the other. For example, over the counter cold remedies exert most of their effects by blocking parasympathetic activity or increasing sympathetic activity that block the action of the sinus fluids which is a parasympathetic response. Sympathetic – increase heart rate
Sensory nerves enter which side of the spinal cord, dorsal or ventral?
Dorsal
Which functions are controlled by the sympathetic nervous system? Which are controlled by the parasympathetic nervous system?
The sympathetic nervous system prepares the organs for vigourous fight-or-flight activity. The parasympathetic system increases vegetative responses such as digestion.
The posterior part of the brain
Hindbrain
Greek root: rhombencephalon
What are the three parts of the hindbrain?
The medulla, the pons, and the cerebellum
The medulla, pons, midbrain, and central structure of the forebrain
Brainstem
Hind brain structure located just above the spinal cord; could be regarded as an enlarged extension of the spinal cord
Medulla
What are the functions of the medulla?
Controls vital reflexes including breathing, heart rate, vomiting, salivation, coughing, and sneezing through the cranial nerves, which control sensations from the head, muscle movements in the head, and much of the parasympathetic output to the organs
Nerves that control sensations from the head, muscle movements in the head, and much of the parasympathetic output to the organs
Cranial nerves
Some of the cranial nerves include both sensory and motor components, where as others have just one or the other. The receptors and muscles of the head and organs connect to the brain by 12 pairs of cranial nerves, one of each pair on the right side and one on the left. Each cranial nerve originates in a nucleus or cluster of neurons, that integrates the sensory information, regulates the motor output, or both.
The cranial nerve nuclei for nerves V through XII are in the medulla and pons. Those for cranial nerves I through IV are in the midbrain and forebrain
Cranial nerve with the function of smell
Olfactory
A cranial nerve related to vision
Optic
A cranial nerve that controls eye movements and pupil constriction
Oculomotor
A cranial nerve that controls eye movement
Trochlear and abducens
A cranial nerve responsible for skin sensations from most of the face; control of jaw muscles for chewing and swallowing
Trigeminal
A cranial nerve responsible for taste from the anterior two thirds of the tongue; control of facial expressions, crying, salivation, and dilation of the heads blood vessels
Facial
A cranial nerve responsible for hearing; equilibrium
Statoacoustic
A cranial nerve responsible for taste and other sensations from throat and posterior third of the tongue; control of swallowing, salivation, throat movements during speech
Glossopharyngeal
A cranial nerve responsible for sensations from neck and thorax; control of throat, esophagus, and larynx; parasympathetic nerves to stomach, intestines, and other organs
Vagus
A cranial nerve responsible for control of neck and shoulder movements
Accessory
A cranial nerve responsible for control of muscles of the tongue
Hypoglossal
Hindbrain structure that lies anterior and ventral to the medulla
Pons
Describe the functions of the pons
Contains nuclei for several cranial nerves. Is Latin for “bridge”, reflecting the fact that in the pons, axons from each half of the brain cross to the opposite side of the spinal cord so that the left hemisphere controls the muscles of the right side of the body and the right hemisphere controls the left side.
The medulla and pons also contain the reticular formation and the raphe system
A structure that extends from the medulla into the forebrain; controls motor areas of the spinal cord and selectively increases arousal and attention in various forebrain areas
Reticular formation
Has descending and ascending portions. The descending portion is one of several brain areas that control the motor areas of the spinal cord. The ascending portion sends output to much of the cerebral cortex, selectively increasing arousal and attention in one area or another
Brain areas that send axons to much of the forebrain, modifying the brains readiness to respond to stimuli
Raphe system
A large hindbrain structure with many deep folds. Long been known for its contributions to the control of movement, balance, and coordination. Also has functions that extend far beyond balance and coordination – people with damage to this area have trouble shifting their attention back-and-forth between auditory and visual stimuli and much difficulty with timing, including sensory timing
Cerebellum
Middle part of the brain
Midbrain
Greek root: mesencephalon
In adult mammals it is dwarfed and surrounded by the forebrain
What are the major structures in the midbrain?
Tectum, tegmentum, superior colliculus, inferior colliculus, substantia nigra
Roof of the midbrain
Tectum
Is the Latin word for roof.
Intermediate level of the midbrain
Tegmentum
Latin word for “covering”. Covers several other midbrain structures, although it is covered by the tectum. Includes the nuclei for the third and fourth cranial nerves, parts of the reticular formation, and extensions of the pathways between the forebrain and the spinal cord or hindbrain
Swelling on either side of the tectum; important to visual processing
Superior colliculus
Swelling on each side of the tectum; important for auditory processing
Inferior colliculus
A midbrain structure that gives rise to a pathway releasing dopamine. This pathway facilitates readiness for movement
Substantia nigra
Most anterior part of the brain; consists of two cerebral hemispheres
Forebrain
Greek root: prosencephalon
Each hemisphere is organized to receive sensory information, mostly from the contralateral or opposite side of the body, and to control muscles mostly on the contralateral side, by way of axons to the spinal cord and the cranial nerve nuclei
What are the major structures of the forebrain?
Thalamus, hypothalamus, cerebral cortex, hippocampus, basal ganglia
What is the outer portion of the cerebral hemispheres called?
Cerebral cortex
Latin for “bark” or “shell”
Interlinked structures that form a border around the brainstem. Important for motivations and emotions, such as eating, drinking, sexual activity, anxiety, and aggression.
Limbic system
Includes the olfactory bulb, hypothalamus, hippocampus, amygdala, and cingulate gyrus of the cerebral cortex
A pair of structures (left and right) in the centre of the forebrain. Most sensory information goes here first, is processed, and the output is sent to the cerebral cortex. An exception is the old factory information, which progresses from the old factory receptors to the factory bulbs and then directly to the cerebral cortex
Thalamus
Many nuclei of the thalamus receive their input from a sensory system, such as vision, and transmit information to a single area of the cerebral cortex. The cerebral cortex sends information back to the thalamus, prolonging and magnifying certain kinds of input at the expense of others, thereby focussing attention on particular stimuli
The thalamus and hypothalamus form the ______, a section distinct from the ________, which is the rest of the forebrain
Diencephalon; telencephalon
Small area near the base of the brain, ventral to the thalamus. Has widespread connections with the rest of the forebrain and the midbrain. Contains a number of distinct nuclei. Conveys messages to the pituitary gland, altering its release of hormones
Hypothalamus
Damage to any hypothalamus nucleus leads to abnormalities in motivated behaviors, such as feeding, drinking, temperature regulation, sexual behavior, fighting, or activity level
An endocrine gland attached to the base of the hypothalamus. Attached to the base of the hypothalamus buy a stock that contains neurons, blood vessels, and connective tissue. In response to messages from the hypothalamus, synthesizes hormones that the blood carries to organs throughout the body
Pituitary gland
A group of subcortical forebrain structures lateral to the thalamus. Includes three major structures: the caudate nucleus, the putamen, and the globus pallidus.
Had subdivisions that exchange information with different parts of the cerebral cortex. Damage to this area impairs movement, as in conditions such as Parkinson’s disease and Huntington’s disease. Also critical for learning and remembering how to do something as opposed to learning factual information or remembering specific events. Also important for attention, language, planning, and other cognitive functions
Basal ganglia
A forebrain structure that lies on the ventral surface; receives input from the hypothalamus and basal ganglia; sends axons to areas in the cerebral cortex. These axons release acetylcholine to widespread areas in the cerebral cortex.
A key part of the brain system for arousal, wakefulness, and attention. Patients with Parkinson’s disease and Alzheimer’s have impairments of attention and intellect because of inactivity or deterioration here.
Nucleus basalis
A large structure located toward the posterior of the forebrain, between the thalamus and the cerebral cortex. Critical for storing certain kinds of memories, especially memories for individual events
Hippocampus
Latin for “seahorse”
People with hippocampal damage have trouble storing new memories, but they do not lose all the memories they had before the damage occurred
A fluid-filled channel in the centre of the spinal cord
Central canal
Four fluid-filled cavities within the brain
Ventricles
A clear fluid similar to blood plasma produced by choroid plexus in the brain ventricles
Cerebrospinal fluid CSF
CSF feels the ventricles, flowing from the lateral ventricles to the third and fourth ventricles. From the fourth ventricle, some of it flows into the central canal of the spinal cord, but more goes into the narrow spaces between the brain and the thin meninges. In one of those narrow spaces, the subarachnoid space, the blood gradually reabsorbs the CSF.
Cerebrospinal fluid cushions the brain against mechanical shock when the head moves. It also provides buoyancy and helps support the weight of the brain. It also provides a reservoir of hormones and nutrition for the brain and spinal cord.
Membranes that surround the brain and spinal cord
Meninges
The meninges have pain receptors – inflammation is painful
Of the following, which are in the hindbrain, which in the midbrain, and which in the forebrain: basal ganglia, cerebellum, hippocampus, hypothalamus, medulla, pituitary gland, ponds, substantia nigra, superior and inferior colliculi, tectum, tegmentum, thalamus?
Hindbrain: cerebellum, medulla, and pons.
Midbrain: substantia nigra, superior and inferior colliculi, tectum, and tegmentum.
Forebrain: basal ganglia, hippocampus, hypothalamus, pituitary, and thalamus.
Which area is the main source of input to the cerebral cortex?
Thalamus
Layers of cells on the outer surface of the cerebral hemisphere of the forebrain
Cerebral cortex
The cells of the cerebral cortex are gray matter, and their axons extending inward are white matter
Bundle of axons that connects the two hemispheres of the cerebral cortex
Corpus callosum and anterior commissure
Order of mammals that includes monkeys, apes, and humans
Primates
The cerebral cortex constitutes a higher percentage of the brain in primates. As the proportion devoted to the forebrain increases in insectivores and primates, the relative sizes of the midbrain and medulla decrease. The cerebellum occupies a remarkably constant percentage – approximately 13% of any mammalian brain
Layer of cell bodies that are parallel to the surface of the cerebral cortex and separated from each other by layers of fibres
Laminae
In humans and most other mammals, the cerebral cortex contains up to six distinct laminae. They vary in thickness and prominence from one part to another, and may be absent from certain areas. Lamina V, which sends long axons to the spinal cord and other distant areas, is thickest in the motor cortex, which has the greatest control of the muscles.
Lamina IV, which receives axons from the various sensory nuclei of the thalamus, is prominent in all the primary sensory areas but absent from the motor cortex
Collection of cells having similar properties, arranged perpendicular to the laminae
Columns
For example, if one cell in a column responds to touch on the palm of the left hand, then the other cells in that column do too
If several neurons of the visual cortex all respond best when the retina is exposed to horizontal lines of light, then those neurons are probably in the same ______
Column
Posterior section of the cerebral cortex. The main target for visual information
Occipital lobe
The posterior pole of the occipital lobe is known as the _____ ______ _____ or striate cortex, because of its striped appearance in cross-section.
Destruction of any part of this area causes ______ ______ in the related part of the visual field.
Primary visual cortex; cortical blindness
For example, extensive damage to the striate cortex of the right hemisphere causes blindness in the left visual field.
A person with cortical blindness has normal eyes and pupillary reflexes, but no conscious visual perception and no visual imagery, not even in dreams. People who suffer I damage become blind, but if they have an intact occipital cortex and previous visual experience, they can still imagine visual scenes and can still have visual dreams
Section of the cerebral cortex between the occipital lobe and the central sulcus. Responsible for body sensations
Parietal lobe
Monitors all the information about eye, head, and body positions and passes it on to brain areas that control movement. Essential not only for spatial information but also numerical information.
One of the deepest grooves in the surface of the cerebral cortex
Central sulcus
Area just posterior to the central gyrus; primary receptor site for touch and other body sensations
Postcentral gyrus
Also known as primary somatosensory cortex
Receives sensations from touch receptors, muscle-stretch receptors, and joint receptors.
Includes four bands of cells parallel to the central sulcus. Separate areas along each band receive simultaneous information from different parts of the body. Two of the bands receive mostly light-touch information, one receives deep-pressure information, and one receives a combination of both. In effect, it represents the body four times.
The lateral portion of each hemisphere, near the temples. It is the primary cortical target for auditory information.
Temporal lobe
The human temporal lobe – in most cases, the left temporal lobe – is essential for understanding spoken language. Also contributes to complex aspects of vision, including perception of movement and recognition of faces. A tumour here may give rise to elaborate auditory or visual hallucinations.
A behavioural disorder caused by temporal lobe damage.
Previously wild and aggressive monkeys fail to display normal fears and anxieties after temporal lobe damage. They put almost anything they find into their mouths and attempt to pick up snakes and lighted matches.
Klüver-Bucy syndrome
Section of the cerebral cortex that extends from the central sulcus to the anterior limit of the brain.
Contains the primary motor cortex and the prefrontal cortex.
Frontal lobe
Posterior portion of the frontal lobe just anterior to the central sulcus; specialized for fine movement control
Precentral gyrus
Specialized for control of fine movements, such as moving one finger at a time. Separate areas are responsible for different parts of the body, mostly on the contralateral side but also with slight control of the ipsilateral side.
Anterior portion of the frontal lobe, which responds mostly to the sensory stimuli that signal the need for a movement
Prefrontal cortex
The dendrites in the pre-frontal cortex have up to 16 times as many dendritic spines as neurons in other cortical areas. As a result, it integrates an enormous amount of information
Which lobe of the cerebral cortex includes the primary auditory cortex?
Temporal lobe
Which lobe of the cerebral cortex includes the primary somatosensory cortex?
Parietal lobe
Which lobe of the cerebral cortex includes the primary visual cortex?
Occipital lobe
Which lobe of the cerebral cortex includes the primary motor cortex?
Frontal lobe
Surgical disconnection of the prefrontal cortex from the rest of the brain
Prefrontal lobotomy
Consequences included apathy, a loss of the ability to plan and take initiative, memory disorders, distractibility, and a loss of emotional expressions. People with damage here also lost their social inhibitions ignoring the rules of polite, civilized conduct. They often acted impulsively because they failed to calculate adequately the probable outcomes of their behaviours
Assignment in which an animal must respond on the basis of a signal that it remembers but that is no longer present
Delayed-response task
People with damage to the prefrontal cortex have trouble with these kinds of tasks, showing problems with a major function of the prefrontal cortex: working memory
What are the functions of the prefrontal cortex?
The prefrontal cortex is especially important for working memory, or memory for what is currently happening, and for planning actions based on the context
For example, deciding to answer the phone when it rings based on the context. You would probably answer it in your own home, but not in someone else’s home.
Question of how various brain areas produce a perception of a single object
Binding problem or large-scale integration problem
Earlier researchers thought that various kinds of sensory information converged on to what they called the association areas of the cortex. Later research found that the association areas perform advanced processing on a particular sensory system, such as vision or hearing, but few cells combine one sense with another.
What is meant by the binding problem, and what is necessary for binding to occur?
The binding problem is the question of how the brain combines activity in different brain areas to produce unified perception and coordination behavior.
Binding requires identifying the location of an object and perceiving sight, sound, and other aspects of a stimulus as being simultaneous. When the site and sound appear to come from the same location at the same time, we bind them as a single experience.
For example, when a skilled ventriloquist makes the dummies mouth move at the same time as his or her own speech, in nearly the same place, you perceive the sound as coming from the dummy
What are the 4 categories that most methods of researching the brain fall into?
- Examine the effects of brain damage
- Examine the effects of stimulating a brain area
- Record brain activity during behaviour
- Correlate brain anatomy with behaviour
Removal of a brain area, and generally with a surgical knife
Ablation
However, surgical removal is difficult for tiny structures far below the surface of the brain
Damage to a structure
Lesion
Used for tiny structures far below the surface of the brain that ablation cannot reach. Researchers use a stereotaxic instrument to make the lesions.
A device for the precise placement of electrodes in the brain
Stereotaxic instrument
By consulting a stereotaxic atlas or map of some species brain, a researcher aims an electrode at the desired position relative to certain landmarks on the skull. Then the researcher anesthetizes the animal, drills a small hole in the skull, inserts the electrode, lowers it to the target, and passes an electrical current just sufficient to damage that area
The application of an intense magnetic field to a portion of the scalp, temporarily inactivating neurons below the magnet
Transcranial magnetic stimulation
Allows researchers to study a given individual’s behaviour with the brain area active, then inactive, and then active again
What is the difference between a lesion and an ablation?
A lesion is damage to a structure. An ablation is removal of the structure. For example, a blood clot might produce a lesion, whereas surgery could produce an ablation
Researchers can insert electrodes to stimulate brain areas in laboratory animals. A new technique _______, enables researchers to turn on Activity in targeted neurons by a device that shines a laser light within the brain
Optogenetics
How do the effects of brief, mild magnetic stimulation differ from those of longer, more intense stimulation?
Brief, mild magnetic stimulation on the scalp increases activity in the underlying brain areas, whereas longer, more intense stimulation blocks it
Why does electrical or magnetic stimulation of the brain seldom produce complex, meaningful sensations or movements?
Meaningful sensations and movements require a pattern of precisely timed activity in a great many cells, not just a burst of overall activity diffusely in one area
A device that records electrical activity of the brain through electrodes attached to the scalp
Electroencephalograph EEG
Electrical recordings on the scalp from brain activity in response to a stimulus
Evoked potentials or evoked responses
A device that measures the faint magnetic fields generated by brain activity
Magnetoencephalograph MEG
Method of mapping activity in a living brain by recording the emission of radioactivity from injected chemicals
Positron-emission tomography PET
A modified version of MRI that measures energies based on hemoglobin instead of water; determines the brain areas receiving the greatest supply of blood and using the most oxygen
Functional magnetic resonance imaging fMRI
Generally has replaced PET scan’s because they are less expensive and less risky
What does fMRI measure?
It measures changes in blood flow to the brain. It detects an increase in blood flow to a brain area immediately after an increase in brain activity, and it also detects a slightly slower increase in the percentage of hemoglobin lacking oxygen
Suppose someone demonstrates that a particular brain area becomes active when people are listening to music. When that area becomes active later, what, if anything, can we conclude?
Without further evidence, we should not draw any conclusion. Perhaps the person is listening to music again, but this area may perform functions other than listening to music. A good test of how well we understand the area would be to find out whether we can use fMRI recordings to guess which type of music someone is hearing or whether they are listening at all
Method of visualizing a living brain by injecting a dye into the blood and placing a persons head into a CT scanner; x-rays are passed through the head and recorded by detectors on the opposite side
Computerized axial tomography CT or CAT scan
From the measurements, a computer constructs images of the brain. Helps detect tumours and other structural abnormalities
Method of imaging a living brain by using a magnetic field and a radio frequency field to make atoms with odd atomic weights all rotate in the same direction and then removing those fields and measuring the energy that the atoms release
Magnetic resonance imaging MRI
By measuring that energy, MRI devices form an image of the brain, and shows anatomical details smaller than a millimetre in diameter. One drawback is that the person must lie motionless in a confining, noisy apparatus
Researchers today sometimes relate differences in people’s behaviour to differences in their brain anatomy. How does their approach differ from that of for phrenologists?
Phrenologists drew conclusions based on just one or a few people with some oddity of behavior. Today’s researchers compare groups statistically. Also, today’s researchers examine the brain itself, not the skull
Why are both brain size and brain-two-body ratio unsatisfactory ways of estimating animal intelligence?
If we consider ourselves to be the most intelligent species, we are confronted with the fact that we have neither the largest rains nor the highest brain-to-body ratios. Brain-to-body ratio depends on selection for thinness as well as selection for brain size. Furthermore, animal intelligence is undefined, so we cannot determine what correlates with it.
Why do recent studies show a stronger relationship between brain size and IQ than older studies did?
The use of MRI greatly improves the measurement of brain size, in comparison to measurement based on the skull
In which way do men and women differ most – intellectual performance, total gray matter, or total white matter?
Men have more white matter, and therefore larger brains. However, men and women are about equal in gray matter and intellectual performance.
