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Hoofdstuk 6 – The neuroscience approach (hoorcollege 8)
Neuroscience is the study of nervous system anatomy and physiology. It is concerned with
both the structure as well as the function of the nervous system in humans and other
animals. As such, neuroscience provides a body of knowledge that serves as a foundation for
understanding how cognitive operations are carried out.
There has been a fairly recent trend in neuroscience toward the integration of
biology with cognition. Out of this union, a new discipline has emerged, called cognitive
neuroscience. The goal of this discipline is to explicate the structures and physiological
processes that underlie specific cognitive functions.
There are many procedures for collecting data in neuroscience. We group these procedures
into three main categories.
1) Investigation of brain damage.
It is unethical to damage a person’s brain to look at the effects of brain damage. For
this reason, researchers examine brain damage and its effects in people for whom
the damage has come about because of an accident – what is called the case study
method.
There is logic behind case studies and lesion studies. If brain area X is damaged and a
deficit is subsequently observed in behaviour Y, researchers infer that area X plays
some role in the control of behaviour Y. Difficulty: Areas of the brain are
interdependent. The effects of damage to one area could have a variety of functional
interpretations. That area could be entirely responsible for a cognitive ability or part
of a collection of areas that mediate that ability. The area could also be a region
through which neural pathways pass as they connect two other brain regions.
2) Recording of brain activities in healthy subjects.
Single-cell recording – a very fine microelectrode is inserted into a single neuron. So
that the changes in that cell’s electrical conductivity or rate of firing can be
measured.
Multiunit recording – a larger electrode is used to measure the collective electrical
activity of a group of neurons.
The electroencephalogram (EEG) – Is a recording of the brain’s gross electrical
action. When large groups of neurons generate synchronized firing patterns, they
produce electric fields that extend out beyond the skull.
Positron emission tomography (PET) – measures blood flow in the brain while a
participant is carrying out a cognitive task. This is accomplished through the use of
radioactive isotopes attached to carrier substances such as glucose or oxygen
molecules. The molecules are injected into the participant’s bloodstream, wherein
they make their way to the brain. Brain areas that are more active during the
execution of a task will show greater regional cerebral blood flow and,
correspondingly, a greater concentration of the tracer molecules bearing the
isotopes.
Functional Magnetic Resonance imaging (fMRI) – detect alterations in local blood
flow and oxygen level. Brain areas that show increases in these measures are those
that have been activated during specific cognitive operations and are therefore
drawing more blood to feed their metabolic processes. So fMRI scans are used to
map out these active brain areas.
, Magnetoencephalography (MEG) – The electric fields that active neurons generate
also have magnetic properties. These magnetic field are measured to determine
patterns of brain activity.
3) Direct stimulation of the brain itself.
This method involves the actual activation of a specific brain area via electrical or
magnetic stimulation. In electrical stimulation, an electrical current is passed through
a bipolar electrode, which causes the neurons of a localized area of brain tissue to
become active. Electrical stimulation encourages neuronal firing, which can result in
positive symptoms. Difficulty: stimulation might induce supranormal activation, or an
overactivation of the region and the areas associated with it. This would produce
behaviors not associated with normal functioning.
In Transcranial magnetic stimulation (TMS), a device with a wire coil is placed over a
person’s head. An electrical current is passed through the coil, inducing a magnetic
field. This field directly causes neurons to fire. If we place the field over different
parts of the cortex, we can witness the functionality of these areas.
Neurons are the microscopic basis of the brain. They are the individual functional units that
perform computations. The purpose of a neuron is to conduct a message in the form of an
electrical impulse. A neuron can be thought of as a link in a complex chain because it
receives incoming messages form thousands of other neurons and then sums those
excitatory (positive) and inhibitory (negative) signals to determine whether it sends an
outgoing message of its own.
Messages are received by the feathery projections known as dendrites. Dendrites
form an extensive branching tree, which connects the neuron to many other neurons. Any
incoming signals picked up by the dendrites are then passed along to the cell body.
Received signals from other cells converge at the axon hillock, where the cell body meets the
axon. Here, the neuron sums all the excitatory and inhibitory inputs it receives. The cell fires
if the sum of these inputs exceeds the cell’s threshold of excitation. This process represents
a substantial change in the neuron’s electrical state. If the threshold is met, an electrical
signal called an action potential is initiated. The action potential the propagates down the
axon, a long tubular structure that projects outward from the cell body. The axon, which can
extend for some distance, ends in a few terminal buttons that meet the dendrites of many
other neurons.
The terminal buttons do not have direct physical contact with the dendrites of the
other neurons. Instead, there is a gap between the two cells known as the synaptic cleft.
How is a message passed from one cell to the next? The answer lies in molecules known as
neurotransmitters. The job of these neurotransmitters is to complete the transmission of
the signal across the synapse.
When the electrochemical action potential arrives at the terminal button, it triggers
the release of neurotransmitters molecules into the synaptic cleft. The transmitters diffuse
across the synaptic cleft and attach to receptor molecules located on the dendritic surface of
the next cell. The receptor molecule activates. These activated receptors then contribute to
the formation of a new signal in the receiving cell that propagates down the dendrite toward
the cell body.
Hoofdstuk 6 – The neuroscience approach (hoorcollege 8)
Neuroscience is the study of nervous system anatomy and physiology. It is concerned with
both the structure as well as the function of the nervous system in humans and other
animals. As such, neuroscience provides a body of knowledge that serves as a foundation for
understanding how cognitive operations are carried out.
There has been a fairly recent trend in neuroscience toward the integration of
biology with cognition. Out of this union, a new discipline has emerged, called cognitive
neuroscience. The goal of this discipline is to explicate the structures and physiological
processes that underlie specific cognitive functions.
There are many procedures for collecting data in neuroscience. We group these procedures
into three main categories.
1) Investigation of brain damage.
It is unethical to damage a person’s brain to look at the effects of brain damage. For
this reason, researchers examine brain damage and its effects in people for whom
the damage has come about because of an accident – what is called the case study
method.
There is logic behind case studies and lesion studies. If brain area X is damaged and a
deficit is subsequently observed in behaviour Y, researchers infer that area X plays
some role in the control of behaviour Y. Difficulty: Areas of the brain are
interdependent. The effects of damage to one area could have a variety of functional
interpretations. That area could be entirely responsible for a cognitive ability or part
of a collection of areas that mediate that ability. The area could also be a region
through which neural pathways pass as they connect two other brain regions.
2) Recording of brain activities in healthy subjects.
Single-cell recording – a very fine microelectrode is inserted into a single neuron. So
that the changes in that cell’s electrical conductivity or rate of firing can be
measured.
Multiunit recording – a larger electrode is used to measure the collective electrical
activity of a group of neurons.
The electroencephalogram (EEG) – Is a recording of the brain’s gross electrical
action. When large groups of neurons generate synchronized firing patterns, they
produce electric fields that extend out beyond the skull.
Positron emission tomography (PET) – measures blood flow in the brain while a
participant is carrying out a cognitive task. This is accomplished through the use of
radioactive isotopes attached to carrier substances such as glucose or oxygen
molecules. The molecules are injected into the participant’s bloodstream, wherein
they make their way to the brain. Brain areas that are more active during the
execution of a task will show greater regional cerebral blood flow and,
correspondingly, a greater concentration of the tracer molecules bearing the
isotopes.
Functional Magnetic Resonance imaging (fMRI) – detect alterations in local blood
flow and oxygen level. Brain areas that show increases in these measures are those
that have been activated during specific cognitive operations and are therefore
drawing more blood to feed their metabolic processes. So fMRI scans are used to
map out these active brain areas.
, Magnetoencephalography (MEG) – The electric fields that active neurons generate
also have magnetic properties. These magnetic field are measured to determine
patterns of brain activity.
3) Direct stimulation of the brain itself.
This method involves the actual activation of a specific brain area via electrical or
magnetic stimulation. In electrical stimulation, an electrical current is passed through
a bipolar electrode, which causes the neurons of a localized area of brain tissue to
become active. Electrical stimulation encourages neuronal firing, which can result in
positive symptoms. Difficulty: stimulation might induce supranormal activation, or an
overactivation of the region and the areas associated with it. This would produce
behaviors not associated with normal functioning.
In Transcranial magnetic stimulation (TMS), a device with a wire coil is placed over a
person’s head. An electrical current is passed through the coil, inducing a magnetic
field. This field directly causes neurons to fire. If we place the field over different
parts of the cortex, we can witness the functionality of these areas.
Neurons are the microscopic basis of the brain. They are the individual functional units that
perform computations. The purpose of a neuron is to conduct a message in the form of an
electrical impulse. A neuron can be thought of as a link in a complex chain because it
receives incoming messages form thousands of other neurons and then sums those
excitatory (positive) and inhibitory (negative) signals to determine whether it sends an
outgoing message of its own.
Messages are received by the feathery projections known as dendrites. Dendrites
form an extensive branching tree, which connects the neuron to many other neurons. Any
incoming signals picked up by the dendrites are then passed along to the cell body.
Received signals from other cells converge at the axon hillock, where the cell body meets the
axon. Here, the neuron sums all the excitatory and inhibitory inputs it receives. The cell fires
if the sum of these inputs exceeds the cell’s threshold of excitation. This process represents
a substantial change in the neuron’s electrical state. If the threshold is met, an electrical
signal called an action potential is initiated. The action potential the propagates down the
axon, a long tubular structure that projects outward from the cell body. The axon, which can
extend for some distance, ends in a few terminal buttons that meet the dendrites of many
other neurons.
The terminal buttons do not have direct physical contact with the dendrites of the
other neurons. Instead, there is a gap between the two cells known as the synaptic cleft.
How is a message passed from one cell to the next? The answer lies in molecules known as
neurotransmitters. The job of these neurotransmitters is to complete the transmission of
the signal across the synapse.
When the electrochemical action potential arrives at the terminal button, it triggers
the release of neurotransmitters molecules into the synaptic cleft. The transmitters diffuse
across the synaptic cleft and attach to receptor molecules located on the dendritic surface of
the next cell. The receptor molecule activates. These activated receptors then contribute to
the formation of a new signal in the receiving cell that propagates down the dendrite toward
the cell body.
