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Learning goals Task 11. How did the understanding of the brain change over time? (historical developments and
shifts because we know we are wrong)
2. What do we know about local functions of the brain?
Chapter 1 Fundamentals of Human Neuropsychology (Task 1)
Neuropsychology is strongly influenced by two experimental and theoretical investigations into brain
function:
- the brain theory (which states that the brain is the source of behaviour)
- the neuron theory (the idea that the unit of the brain structure and function is the neuron).
1.1. The Brain Theory
What is the brain?
The brain is the tissue found within the scull. The two almost symmetrical
halves of the brain are called hemispheres. The brain’s basic plan is that of a
tube filled with salty fluid called cerebrospinal fluid (CSF). This cushions the
brain and assists in removing metabolic waste. The “bark” of the brain is the
cerebal cortex which consists of gyri (the bumps in the cortex) and sulci (the
creases between the bumps). Some large sulci are called fissures: the
longitudinal fissure divides the two hemispheres and the lateral fissure
divides each hemisphere into halves. The large pathway (commissure) in the
brain that connects the two hemispheres is called the corpus callosum.
The cortex of each hemisphere forms four lobes, each named after the skull bones beneath which
they lie. The temporal lobe is located below the lateral fissure. Lying immediately above the temporal
lobe is the frontal lobe. The parietal lobe is located behind the frontal lobe, and the occipital lobe
constitutes the area at the back of each hemisphere.
The cerebral cortex constitutes most of the forebrain. The remaining “tube” underlying the cortex is
the brainstem. The brainstem is in turn connected to the spinal cord. This three-part brain is
conceptually useful evolutionarily, anatomically, and functionally.
How does the brain relate to the rest of the nervous system?
The brain and spinal cord together are called the central nervous system. The CNS
is connected to the rest of the body trough nerve fibers. Some fibers carry
information away fron the CNS; others bring information into it (the peripheral
nervous system). The PNS tissue will regrow after damage, whereas the CNS does
not regenerate lost tissue.
1.2. Perspectives on the brain and behaviour
The central topic in neuropsychology is how brain and behaviour are related. There are three classic
theories - mentalism, dualism, and materialism:
Aristotle: Mentalism
Aristotle was the first person to develop a formal theory of behaviour. He proposed that a
nonmaterial psyche is responsible for human thoughts, perceptions, and emotions and for such
processes as imagination, opinion, desire, pleasure, pain, memory, and reason. The psyche is
independent of the body, but it works through the heart to produces action. The philosophical
position that a person’s mind is responsible for behaviour is called mentalism.
,Descartes: Dualism
Descartes wrote the first neuropsychology text. Descartes saw the mind as something different from
the body. The body operated on principles similar to those of a machine, but the mind decided what
movements the machine should make. He located the site of action of the mind in the pineal body
(now called the pineal gland). Descartes’s position that mind and body are separate but can interact
is called dualism, to indicate that behaviour is caused by two things. Dualism is known as the mind-
body problem.
Darwin: Materialism
The idea of materialism is that rational behaviour can be fully explained by the workings of the
nervous system. No need to refer to a nonmaterial mind. Darwin and Wallace support the idea that
living things must be related. Natural selection is Darwin’s theory for explaining how new species
evolve and how they change over time. A species is a group of organisms that can breed among
themselves but usually not with members of other species. Individual organisms within a species vary
in their phenotype, the traits we can see or measure. The unequal ability of individual organisms to
survive and reproduce is related to the different genes they inherit from their parents and pass on to
their offspring. Mendel realized that the environment plays a role in how genes express traits. The
science that studies differences in gene expression related to environment and experience is
epigenetics. Epigenetic factors do not change the genes individuals inherit, but they do affect
whether a gene is active – turned on or off – and in this way influence an individual’s phenotypic
traits.
Contemporary perspectives
Contemporary theory is both materialistic and neutral with respect to beliefs, including religious
beliefs. Today, when neuroscientists use the term mind, most are not referring to a nonmaterial
entity but using it as shorthand for the collective functions of the brain.
1.3. Brain function: insights from brain injury
Localization of function
The first general theory to propose that different parts of the brain have different functions was
developed in the early 1800s by German anatomist Franz Josef Gall and Johann Casper Spurzheim.
They proposed that the cortex and its gyri were functioning parts of the brain and not just coverings
for the pineal body. They supported their position by showing through dissection that the brain’s
most distinctive motor pathway, the corticospinal (cortex to spinal cord) tract, leads from the cortex
of each hemisphere to the spinal cord on the opposite side of the body. Thus, according them, the
cortex sends instructions to the spinal cord to command muscles to move. They also recognized that
the two symmetrical hemispheres of the brain are connected by the corpus callosum and can thus
interact. Gall developed his hypothesis, called localization of function, that a different, specific brain
area controls each kind of behaviour. They furthered this idea by proposing that a bump on the skull
indicated a well-developed underlying cortical gyrus and therefore a greater capacity for a particular
behaviour. They assigned each trait to a particular part of the skull and, by inference, to the
underlying brain part. Spurzheim called this study of the relation between the skull’s surface features
and a person’s mental faculties phrenology.
Lateralization of function
It now is clear that for example language is both localized in the brain and lateralized, that is, located
on one side of the brain. One cerebral hemisphere can perform a function not shared by the other.
Bouillaud argued from clinical studies that certain functions are localized in the cortex and,
specifically, that speech is localized in the frontal lobes, in accordance with Gall’s theory. He also
suggested that the part of the brain that controls acts such as writing, drawing, painting and fencing
might be the left hemisphere. Phisicians had long recognized that damage to a hemisphere of the
brain impairs movement of the opposite side of the body. Paul Broca received a patient who only
,was able to say the wordt “tan”. The right side of his body was paralyzed, but he seemed intelligent
and typical in other respects. Tan should have a frontal lesion. This proves that Auburtin was correct:
the left frontal lobe was the focus of Tan’s lesion. Broca located speech in the third convolution
(gyrus) of the frontal lobe on the left side of the brain. The anterior speech region of the brain is now
called Broca’s area, and the syndrome that results from its damage is called Broca’s aphasia.
A lateralized language model
German anatomist Carl Wernicke created the first model of
how the brain produces language in 1874. He suspected a
relation between hearing and speech functioning, and he
described cases in which aphasic patients had lesions in this
auditory area of the temporal lobe. They could speak
fluently, but what they said was confused and made little
sense. Wernicke’s syndrome is sometimes called temporal-
lobe aphasia or fluent aphasia, to emphasize that the
person can say words, but is more frequently called
Wernicke’s area. The arcurate fasciculus is a pathway from
Wernicke’s area to Broca’s area. Representations of speech
movements are stored in this area and may link brain
regions related to intelligence. According to Wernicke’s model, if the temporal lobe is damaged,
speech movements are preserved in Broca’s area, but the speech makes no sense because the
person cannot monitor words. Damages to Broca’s area produces a loss of speech movements
without the loss of sound images, and therefore Broca’s aphasia is not accompanied by a loss of
understanding.
Disconnection
Wernicke suggested that, if the arcuate fibers connecting the two speech areas were cut,
disconnecting the areas but without inflicting damage on either one, a speech deficit that Wernicke
described as conduction aphasia would result. In this condition, speech sounds and movements are
retained, but speech is impaired because it cannot be conducted from one region tot the other. The
patient would be unable to repeat what is heard. Wernicke’s idea of disconnection offered
investigators a completely new way of viewing symptoms of brain damage by proposing that,
although different brain regions have different functions, they are interdependent: to work, they
must interact. This leaded to found patients with alexia and apraxia, because they appear trough
disconnection.
Disconnection is important in neuropsychology, first because it predicts that complex behaviours are
built up in assembly-line fashion as information collected by sensory systems enters the brain and
traverses different structures before producing an overt response. Second, disconnecting brain
structures by cutting connecting pathways can impair those structures in ways that resemble damage
to the structures themselves.
Neuroplasticity
Flourens and Goltz challenged the idea that brain functions are localized. Both men created animal
models of human clinical cases by removing small regions of cortex. Both expected that the animals
would lose specific functions. Goltz did a terrible research by removing the cortex of three dogs and
studied the dogs until they all died. These early experiments actually built the foundation for
neuropsychology’s emphases on recovery of function and on promoting recovery by rehabilitation
after brain damage, even in extreme circumstances. Neuropsychologists recognize that, although all
function may not be recovered after injury, the brain’s plasticity can be harnessed to produce
significant functional improvements.
, Hierarchical organisation
Goltz and Flourens made a strong argument against localization of function and even cast doubt on
the role of the cortex in behaviour. An explanation for the apparent disconnect between experiments
that support functional localization and those that observe recovery of function is hierarchical
organization. English neurologist John Hughlings-Jackson proposed this principle of cerebral
organisation in which information is processed serially and organized as a functional hierarchy. Each
successively higher level controls more-complex aspects of behaviour and does so via the lower
levels. Hughlings-Jackson’s theory gave rise to the idea that functions are not simply represented in
one location in the brain but are re-presented in the neocortex, in the brainstem, and in the spinal
cord. Thus, understanding a function such as walking requires understanding what each level of
organisation contributes to that behaviour.
Multiple memory systems
The conclusion from more than six decades of study is that many memory systems operate within
the brain. The research began with removing parts of the temporal lobes from the left and right
hemispheres of patient H.M. to treat his epilepsy (condition with recurrent seizures associated with
disturbance of consciousness). The surgery stopped the epilepsy but left H.M. with a severe memory
problem: amnesia (partial or total loss of memory. Rather than a single memory structure in the
brain, a number of neural structures encode memories separately and in parallel. Thus, it
demonstrate that the neural structures for learning motor skills and those for remembering that one
has those skills are separate. The study of amnesia suggests that when people have a memorable
experience, they encode different parts of the experience in different parts of the brain concurrently.
How does the brain tie single and varied sensory and motor events together into a unified perception
or behaviour, or a memory? This binding problem extends from perceptive to motor to cognitive
processes, the different parts of which are mediated by different neural structures.
Two brains
To prevent the spread of intractable epileptic seizures from one hemisphere to the other in a number
of patients the corpus callosum and the smaller commissures that connect the two cortical
hemispheres are cut. It improves the lives of the patients and it reduces the seizures. Each
hemisphere possesses complementary self-awareness and social consciousness and that much of
internal mental life, especially in the right hemisphere, is inaccessible to analysis using spoken
language.
Conscious and unconscious neural streams
The brain lesions in agnosia patients occur in neural structures that constitute a pathway, called the
ventral stream, from the visual cortex to the temporal lobe for object
identification. Brain lesions in patients with optic ataxia are in neural structures
that form a pathway from the visual cortex to the parietal cortex called the
dorsal stream to guide action relative to objects. The ventral stream is for
conscious visual perception, the dorsal stream is for unconscious visual
processes. It follows that other sensory systems are not unitary but rather
consists of separate pathways that mediate unconscious or conscious actions.
The paradox posed by the discovery of conscious and unconscious vision is that
in its goal to account for our conscious behaviour, neuropsychology must also
identify and account for our unconscious behaviour.
1.4. The neuron theory
The second major source of findings that influences modern neuropsychology is
the neuron theory, the idea that the unit of brain structure and function is the
nerve cell.
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