Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_123_библиотеки_им_акад_М_И_Перельмана
.pdf
CHAPTER 17 Thinking About Intelligence, Language, and Lateralization 321
Chapter17
Thinking About
Intelligence, Language,
and Lateralization
L
anguage, consciousness, and thought are uniquely human traits. (However,
if your dog can ask for their dinner in full sentences, please post the video
online and send us the link.) Cognitive functions and consciousness are
impressive abilities. How a brain only about twice the size of a chimpanzee’s but
smaller than a dolphin’s or elephant’s developed these abilities is unclear,
although many theories exist. This chapter looks at the basis of language. We also
discuss the notion of intelligence and consider that mysterious but important fea-
ture that’s quite special to humanity— consciousness.
Cognitive functions refer to mental abilities and processes involved in the acquisi-
tion of knowledge, manipulation of information, and reasoning. They include
attention, perception, executive functions (see Chapter16), learning and memory
(check out Chapter15), and language abilities (which we discuss here). Cognitive
IN THIS CHAPTER
»
Noting the brain areas that allow for
language
»
Following pathways of thought
»
Saying what’s on your mind in both
brain hemispheres
»
Knowing what intelligence means
»
Being emotionally intelligent
»
Exploring consciousness
https://t.me/med1917
322 PART 3 Understanding Perception and Cognition
functions involve multiple interconnected cortical brain regions, are interdepen-
dent, and are the basis of intelligence, the ability to acquire and apply knowledge
and skills. Many scientists also predict that consciousness emerges from complex
interactions among cognitive functions.
Adapting the Human Brain for Language
Language requires a brain that can perform complex sensory processing, execute
complex behavior, and communicate by utterances and postures (body language).
Somewhere along the lines of evolution, the human brain adapted complex lan-
guage capabilities. Here we look at the major organizational features of the brain
that adapted for thought, language, and consciousness.
Finding how the brain is organized
If you look at the brain as a collection of 86 billion neurons, each with a thousand
synapses, the possibility of truly understanding the brain seems hopeless. How-
ever, knowing four principles of brain organization is a good start to understand-
ing how the brain works:
»
Neuron types are countable. Usually less than 100 dierent types of
neurons are found in any particular region of the central nervous system.
»
Neuronal circuits tend to have similar structures even in dierent areas
of the brain. Once the neocortex evolved in mammals, its layered structure
has remained the same in all mammals, including humans. Primate and
human brains increased in size through addition of new areas of neocortex.
All neocortex is thought to contain essentially the same neural circuitry,
repeated in millions of minicolumns.
A minicolumn is a vertical column in neocortex containing about 100 to 200
neurons. Neurons in a minicolumn receive common inputs, have common
outputs, and are interconnected. Many neuroscientists consider minicolumns
to be the fundamental computational unit of the neocortex.
»
The brain works using a small world of connections. Local connections are
much denser than those over long distances. Having most processing happen
over short distances means the brain is modular and compact. Results of
connections are shipped over a relatively small numbers of output axons to
other cortical, brain or spinal cord regions.
https://t.me/med1917
CHAPTER 17 Thinking About Intelligence, Language, and Lateralization 323
»
The brain is hierarchical. Hierarchical cortical organization has been shown
in sensory, memory and reward systems. Adjacent cortical areas in the
hierarchy are connected by strong forward connections, with weaker, but
important feedback projections. High-level controllers can also control
low-level controllers, like a home’s thermostat that operates the furnace and
air conditioner to maintain the temperature.
To understand the brain, you need to understand how a nite number of basic
types of neurons work, how these neurons operate in a nite number of neural
circuits, what the dierent processing modules are (a nite number), and how the
overall control scheme is laid out. Of course, this sounds simpler than it actually
is, but these principles are much easier to understand than trying to tackle 86 bil-
lion neurons, each with a thousand of synapses.
Contemplating with the neocortex
Many scientists believe (or assume) that whatever dierentiates human brains
(which have consciousness) from nonconscious brains resides in the neocortex.
This assumption is based on the fact that neocortical expansion dierentiates
mammals from nonmammals, primates from other mammals, and humans from
primates. It’s also based on the fact that in the case of language— which enables
consciousness— damage to specic brain areas (Wernicke’s and Broca’s areas)
causes specic language problems.
Assuming that neocortical expansion alone is responsible for consciousness may
not be entirely correct. The cerebellum, for example, expanded considerably in
primates and humans compared to other mammals. But even if unique human
abilities originated in some changes in the neocortex, they cascaded into changes
in subcortical structures as well.
The neocortex is the place to start looking for the basis of higher cognitive func-
tions. Taking a top-down view of the brain starts with the four major lobes of the
neocortex: frontal, parietal, temporal, and occipital. The frontal lobe organizes
motor output and produces executive functions, while the other three lobes pro-
cess sensory information and interact with the frontal lobe to store long-term
memory. The parietal, temporal, and occipital lobes project to subcortical struc-
tures and to the frontal lobes as part of behavior generation.
One of the most baing facts about the neocortex is that its structure is very sim-
ilar in all parts of the brain in all mammals. Some dierences, such as neuronal
densities do exist, but the fundamental minicolumn circuitry is mostly the same.
Therefore, something about this basic processing architecture very well may ena-
ble consciousness.
https://t.me/med1917
324 PART 3 Understanding Perception and Cognition
Processing in gray matter
The neocortex has six layers and is made up of gray and white matter (refer to
Chapter11). The 3- to 5-millimeter layer of gray matter is where the cell bodies
and dendrites of the neurons do most of the processing. White matter beneath is
composed of axons that mediate cortical-to-cortical and cortical–to-subcortical
connections (in both directions).
Transmitting in white matter
Neocortex expanded in two major ways during mammalian and primate
evolution:
»
Increase in area: The increase of the neocortical area occurred through the
addition of minicolumns rather than adding single neurons. Increasing the
number of canonical cortical minicolumn circuit areas eventually caused the
cortex to become convoluted, with gyri and sulci, to t inside the skull— like
wadding up a piece of paper to cram it in a coee cup.
»
Increase in white matter: The brain needed more interconnections as the
number of neurons increased. Interconnections ultimately limit brain size.
Each cortical neuron has a few thousand output synapses in a brain of 86
billion other neurons.
The physical limits of connectivity for 86 billion neurons results in the small
world principle of neocortical connectivity. The neocortex is composed of gluta-
matergic excitatory neurons and GABAergic inhibitory neurons. Most connections
in a minicolumn are local and involve excitatory and inhibitory neurons that are
only connected in one minicolumn. A small percentage of excitatory pyramidal
neurons constitutes the output of the minicolumn, and even then most of their
connections are within a few hundred micrometers. Only a small percentage of
neocortical pyramidal neurons project centimeters or more. This occurs in a fairly
limited number of major axon tracts, the identication of which is a goal of con-
nectome projects run by the National Institutes of Health and the Allen Institute.
Sensory processing in parietal, temporal,
and occipital lobes
The ve senses are processed in the parietal, temporal, and occipital lobes. How-
ever, research shows that these areas aren’t purely sensory.
Throughout this book we often refer to these lobes as “sensory,” but that’s an
oversimplication. (When it comes to the brain, nothing is ever simple.) Process-
ing and integration of sensory information is necessary for determining which
motor behaviors to execute or which actions to take.
https://t.me/med1917
CHAPTER 17 Thinking About Intelligence, Language, and Lateralization 325
For example, blind people, who have no retinal output to drive the occipital lobe,
activate this lobe when identifying objects by touch, which requires internally
representing the object’s shape and layout. Research has shown that the ring of
neurons in V1 (visual area 1— refer to Chapter13) depends on what an animal,
such as a monkey, does depending on the visual information. That is, V1 responses
are dependent on dierent actions being executed.
One remarkable aspect of sensory cortical connectivity is that areas that project
“upstream” in the processing hierarchy, such as V1 to V2, typically receive an
almost equal reciprocal connection. Primary sensory areas (such as V1, S1, and A1)
that receive inputs from the thalamus also project back to the thalamus. Reticular
and higher-order thalamic areas can modulate activity in all primary projection
pathways.
Through the feedback connections, high-level sensory areas can drive lower-level
sensory areas. High-level sensory areas can themselves be driven by the frontal
lobe, a motor control lobe. So, motor behavior possibilities can modulate sensory
processing. This improves what you need to see and hear to carry out the task
you’re doing.
Specializing for memory
A common misconception is that memory in the human brain works like the
memory of a computer. In computers, memory is a data string stored in a specic
location. It has an address so the data can be stored and retrieved when needed.
But in the human brain, memory involves modication of the synapses of neurons
that were active when the memory was created. This allows humans to, in a way,
re-create and reestablish the original brain circuit activity associated with the
memory. (We discuss memory in Chapter15.)
Many animals, including invertebrates, have long-term memories that last for
days, months, or years. Mammals use the hippocampus to encode declarative,
explicit memories from short-term to long-term memory.
For declarative, explicit memory, sensory areas provide input to the entorhinal
cortex, which then transmits that information to the hippocampus. Neurons in
the hippocampus project back to the neocortical areas that activated them. Inter-
play between hippocampal and neocortical activity reproduces important aspects
of the information to be remembered in the neocortex that initially represented
that information. Synapses in the neocortex are modied so that the cortex can
re-create the to-be-remembered state, even if the hippocampus is removed.
Studies and empirical observations indicate that declarative memory is also asso-
ciated with consciousness. Both the formation and retrieval of semantic and
episodic memories are linked with phenomenal awareness.
https://t.me/med1917
326 PART 3 Understanding Perception and Cognition
The sensory areas of the neocortex, then, process sensory information not only
contingent on its motor use, but also based on prior experience, such as, memo-
ries. This whole process is very dierent from the way standard computers work.
Following Thought through Sensory
Pathways and Hierarchies
To better understand the neocortex, you need to look at its relation to and depend-
ence on the thalamus. Virtually all sensory input— except for a major olfactory
pathway— relays through the thalamus to reach the cortex. Thalamic relays also
control motor programs in the frontal lobes.
Sensory and motor cortical areas also project back to the thalamus. The thalamus
integrates activities from various cortical areas. Considerable evidence indicates
that awareness in humans and animals depends on the circuit by which the pre-
frontal sensory neocortices interact through the thalamus. To understand this
circuit, consider how the thalamus controls neocortical function, which we explore
in the following sections.
Relaying to the thalamus and cortex
Although human memory and computer memory work quite dierently, you can
use another computer metaphor to understand the interaction between the thal-
amus and neocortex. This is called the subroutine.
In a well-organized computer program, a main program sequences the major
steps in the computation. This main program calls subroutines or functions for
more detailed calculations, and the results are returned to the main routine
sequence. Of course, the subroutines themselves may call other, even lower-level,
routines.
Taking the visual system as an example, about 1 million retinal ganglion cell axons
project to the lateral geniculate nucleus of the thalamus on each side of the brain.
About the same number of thalamic relay neurons project to V1, where they
directly drive 100 to 200 times that many neurons in V1 alone. V1 projects to higher
visual areas like V2, but also back to thalamus, as do the higher areas. The projec-
tion and return from the thalamus to the neocortex works like a computer pro-
gram’s subroutine call with the thalamus running the main program and the
neocortex computing details.
https://t.me/med1917
CHAPTER 17 Thinking About Intelligence, Language, and Lateralization 327
Projecting back to the thalamus
Thalamic neurons are often called relay cells because their receptive elds are sim-
ilar to those of the inputs they receive from sensory areas. But neocortical sensory
areas contain neurons with more complex and specic response properties than
primary thalamic recipient areas like V1. This plan continues in higher-order sen-
sory processing areas.
The reciprocal projection from cortex back to thalamus modulates the thalamic
output. For example, say a linear feature in a visual image is weak because of blur
or some other object obstructing the feature. Line or edge detectors in the cortex
may activate and enhance the ring of the thalamic cells along that line to increase
its neural contrast.
One way that neural contrast is increased in the thalamic output appears to be by
correlated ring. The tendency for neurons to re at the same time for some visual
input to which they are responding.
Figure17-1 shows how correlated ring works. On the left are the responses of a
retinal ganglion cell to repetitions of a ash of a small spot. This is called a raster
plot. Each vertical hash mark represents an action potential that occurred during
the one-second recording time after the spot was turned on.
Like virtually all sensory neurons in all brains, the responses elicited by repeti-
tions of an identical stimulus are similar but not identical for each repetition. At
the bottom of the raster plots is the peri- (or post-) stimulus time histogram
(PSTH). It’s the sum or average of all spikes for all stimuli in a sequence of time
bins (typically 20 milliseconds).
The idea that the spike pattern doesn’t convey information because the responses
appear to vary randomly has been overturned in the last decades. The right of
Figure17-1 illustrates a hypothetical set of rasters and PSTHs. In the left column
(Stimulus 1), two cells, A and B, show typical response variability. Their PSTHs are
shown at the bottom. The asterisks in the second and third stimuli rasters show
occasions where spikes in the two cells happened to occur at the same time.
In the right column (Stimulus 2), the spikes have been arranged slightly among
the stimuli so that the PSTHs remain unchanged. However, now the number of
correlated responses, denoted by the asterisks, is much higher. Recording from
one cell at a time wouldn’t reveal the dierences between the ring correlation
dierences between stimulus sequence 1 and 2. But in stimulus sequence 2 there’s
much higher correlated ring.
https://t.me/med1917
328 PART 3 Understanding Perception and Cognition
The importance of correlated ring is that cells A and B would be much more
likely to result in spike production by the postsynaptic target when the spikes
occurred at nearly exactly the same time, as in sequence 2, versus not so, as in
sequence 1.
Correlated ring can elevate a small percentage of activity in the brain above the
background of all the rest of the neural activity. Numerous mechanisms exist by
which the spike the spike timing of neurons can be adjusted to select some activity
to aid in brain development or general brain awareness.
An important function of feedback between cortical areas and between cortical
and subcortical structures (such as the thalamus) is to increase correlated ring
for sensory input that is important or that needs to be attended to. Correlated
ring is a major mechanism of attention. It can integrate and select neural activity
across the entire brain. Considerable evidence exists that correlated ring under-
lies all brain activity you’re conscious of.
Gating and integrating functions
The other major modulator of thalamic activity is through reticular zones within
the thalamus that are connected to the reticular formation in the brainstem (refer
to Chapter 10). They modulate signals going through the thalamus and may
change activity in one area of the thalamus within one sense (for example,
FIGURE17-1:
Correlated ring.
© John Wiley & Sons, Inc.
https://t.me/med1917
CHAPTER 17 Thinking About Intelligence, Language, and Lateralization 329
enhancing the neural activity coding for red things if you’re looking for some-
thing red) or between senses (enhancing vision at the expense of audition).
The thalamus doesn’t drastically change the character of the sensory and motor
information relayed through it. But it does modulate that activity through corre-
lated ring and other mechanisms to enhance some information at the expense of
the rest. In other words, it mediates attention.
This attention mechanism depends on processing in the cortex itself, which
includes long-term memory changes in the cortex that are induced by experience
and frontal lobe representations of current goals and contingencies.
Speaking Your Mind: Language, Vision,
and the Brain Hemispheres
Language sets humans apart from all other animals, and it’s more than commu-
nication. Language is a symbolic system that uses rule-based grammar to enable
almost innite expressivity not only for communication, but also for thought and
memory itself. Consider that, after you walked through a room, someone could
ask you what was in it. You might reply you saw two lamps, a table, some chairs.
When asked to describe these items in more detail, like their colors, design
scheme, and so forth, you might not be able to provide much more information.
Your brain eciently stored the verbal labels of the items, not all the details of
their composition.
Specialized brain regions — on the left side in most people — mediate the
understanding and production of language. Damage to these areas can result in
language-specic dysfunctions. The right hemisphere of the brain also has spe-
cial capabilities for certain types of holistic processing, notably visual representa-
tions of images. Dierent processing styles of the left and right hemispheres of
the brain lead to unique human capabilities.
The following sections describe the characteristics and areas of the brain involved
in language.
Comparing communication and language
One of the most persistent sources of debate in neuroscience and related elds—
such as psychology, anthropology, sociology, and even philosophy— is the rela-
tion between animal communication, human language, and consciousness. Why is
language so special?
https://t.me/med1917
330 PART 3 Understanding Perception and Cognition
Animals communicate. Insects communicate via pheromones, and birds and
monkeys carry on extensive and elaborate verbal communication. Some dogs have
been shown to recognize more than 100 words. And some chimpanzees have
coined novel multi-word utterances such as “water bird” for duck.
The dierence between language and other types of communication is grammar.
Think of the dierence between arithmetic and algebra. Arithmetic allows you to
count things and put them in order. Algebra allows you to represent abstract rela-
tionships and to manipulate those abstract relationships using equations.
Communication systems based on hundreds of verbalizations have only as much
power as the number of words. A grammatical language, however, can represent
relationships between what the words stand for and relationships between rela-
tionships, such as the relationship between the self and another relationship. As
caveman Og might say, “We avoid path with hungry tiger.”
Internal vocalizing enables consciousness. Thoughts consist of symbolic repre-
sentations of reality through words and grammar. Thoughts form specic memo-
ries that can be retrieved and related to one’s current situation. This doesn’t mean
that nonverbal thought doesn’t exist, but only that its power to guide behavior is
very limited unless the thought is embedded in the complex verbally based repre-
sentation of the world.
Locating language in the brain
The primary language areas (Wernicke’s area and Broca’s area) are located in the
left hemisphere in 95 percent of all right-handed people and the majority of left-
handed people. The language hemisphere is also usually the dominant hemisphere
for eye dominance.
Figure17-2 shows the left hemisphere of a human brain from the side. Wernicke’s
area is at the junction of the temporal and parietal lobes at the posterior section of
the superior temporal gyrus, typically associated with Brodmann area 22. This is
a high-order auditory processing area necessary for understanding language and
producing language that is coherent.
Broca’s area (typically associated with Brodmann area 44) contains the neural
machinery for producing language. This frontal lobe area is part of the premotor
cortex area, which is next to areas of primary motor cortex that control the tongue,
lips, and vocal cords— all necessary for producing language.
https://t.me/med1917
Соседние файлы в папке Библиотека им академика М.И. Перельмана