Neuropsychology: Anatomy of the Brain · 2013. 2. 14. · Neuropsychology: Anatomy of the Brain Neuropsychology seeks to understand the functions of different parts of the brain,

Neuropsychology Embla, Erika, Edvin, Elin, Fredrika and Farhana

Neuropsychology: Anatomy of the Brain

Neuropsychology seeks to understand the functions of different parts of the brain, by looking at the structure of the brain in a clinical or scientific way. Neuropsychology is physical and seeks to treat behaviors directly associated with brain functioning. This study sheet will tell you about the most important parts of the brain.

The Cerebral Cortex

The cerebral hemispheres are covered with a thin layer of gray matter, called the cerebral

cortex. The cerebral cortex is the highest developed part of the brain and is responsible for higher

brain functions such as sensation, perception, voluntary muscle movement, thought, reasoning

and memory. Most information we perceive is processed in the functional areas of the cerebral

cortex. The gray surface of the cerebral cortex is made up of nerve cells. Underneath the nerve

cells can we find white fibers which carry signals between the nerves and other parts of the body.

Moreover, the cerebral cortex is divided into four lobes roughly defined by the foremost folds on

the surface of the brain, at times the limbic system – or limbic lobe – is considered to be a fifth

lobe. In short, one can definitely state that the cerebral cortex is important for a wide range of

different functions, all from basic drives for self-preservation to the highest level of consciousness.

The Hemispheres

The cerebral cortex covers the two cerebral hemispheres, known as the left and right

hemispheres. The two hemispheres look symmetrical, but each side functions rather differently.

The right hemisphere is most often connected with creativity whilst the left tend to be associated

with logic abilities. Of course that is not always the case, but a generalization, the two

hemispheres work together, are connected and share information through the corpus callosum.

The corpus callosum is a bundle of nerve fibers which connects the two hemispheres; however the

cerebral hemispheres are also connected by a smaller band of nerve fibers called the anterior

commissure. Both hemispheres are concerned with the control of muscles and sensory input from


the opposite side of the body. Therefore, damage to one side of the brain will affect the opposite

side of the body.

A lot of what we know about the two hemispheres comes from studies of people who have had

their corpus callosum split. This operation isolates most of the right hemisphere from the left, and

vice versa. This type of surgery is performed in patients suffering from epilepsy, where the corpus

callosum is split to prevent the spread of the “epileptic seizure” from one hemisphere to the

other.

Dominant Functions

Left Hemisphere:

o Language o Math o Logic

Right Hemisphere:

o Spatial abilities o Face recognition o Visual imagery o Music

The Neocortex

The neocortex takes up the bulk of the cerebrum. It is a six layered structure of the cerebral

cortex which is only found in mammals. The neocortex is believed to be a quite recently evolved

structure, and is associated with intellectual processing of information in more fully evolved

animals (e.g. Humans, primates and dolphins).

The Visual Cortex

The primary visual cortex is the area of the neocortex which has been particularly well studied. It is found in the back of the occipital lobe, mainly on the balks of a deep sulcus. The eyes send signals to the visual field via the thalamus.

The Primitive Cortex A more ‘primitive’ cortex is the hippocampus (named after its appearance in cross-section) which is to be found underneath the inner aspect of the temporal lobe. The structure of it is rather simple compared to the neocortex, with only three layers. The hippocampus receives the processed information from the association cortex, and is also believed to be involved in the short-term conscious memory. Functionally it is connected with the hypothalamus and the limbic system, which are the parts of the brain that control basic functions such as hormonal systems and basic body rhythms and appetites.

Brainstem the autopilot of your body

The brainstem is located at the base of the brain as a continuation of the spinal cord and underneath the limbic system, it lies between the cerebral hemispheres. The brainstem houses control centers for vital body functions such as swallowing, breathing


and the beating of the heart. Almost all cranial nuclei are located here, providing motor and sensory functions to structures of the cranium. The brainstem is said to be the simplest part of the brain and resembles animal brains. It is a neural structure and a part of the nervous system, most cranial nerves originate from the brainstem.

3 Main Parts

Medulla Oblongata (Myelencephalon) The Medulla Oblongata is placed in the lower part of the brain where it connects to the spinal cord, it is a crossing tract between spinal cord and brain. The Medulla is the reflex center for swallowing, coughing, sneezing, vomiting and the respiratory center for breathing. Nerves go from the Medulla connecting to the ears and facial muscles.

Pons (Metencephalon) It is a "bridge", or a band of nerve fibres, linking Medulla Oblongata and the Cerebellum with the Midbrain. The pons conain nuclei which relay signals from the forebrain to the cerebellum along with nuclei which deal with sleep, respiration, swallowing, facial expressions and so on.

Midbrain (Mesencephalon) The midbrain is placed, as you can hear by the name, in the middle of the brain. It is a nerve pathway of cerebral hemispheres and it contains audio and visual reflex centers.

Cerebellum The cerebellum is the second largest part of the brain (the cerebrum being the largest). It is located at the bottom of the skull above the brainstem and beneath the cerebral cortex. It is comprised, in a similar way to the cerebral cortex, of an inner layer consisting of white matter and thinner, outer layer of grey matter. The outer layer is called cerebellar cortex.

Function

The cerebellum could be divided into three parts;

1. Vestibulocerebellum – mainly taking care of balance but also movement of head and eyes.

2. Spinocerebellum – regulates body and limb movements

3. Cerebrocerebellum – regulates planning and timing movements

The cerebellum contains of 50% of the central nerve system’s nerve cells and uses these hundreds of millions of neurons to process data between body muscles and areas of the cerebral cortex. Motor neurons make it possible for us to respond to our environment and some responses are voluntary (e.g. “We see the door to our house, choose to open that door, and enter.”) and others are involuntary (e.g. “We hear the sound of a window breaking, interpret this as an unusual (and perhaps frightening) event, and our heart begins to race.”). Parts of the cerebellum works together with the cerebrum to regulate involuntary responses.

The cerebellum is responsible for motor control and equilibrium. However, it does not initiate movement but it does contribute to coordination, precision and accurate timing. It may also be involved in some cognitive functions such as language, attention and in regulating fear and


pleasure responses. A damaged cerebellum could lead to:

Loss of coordination of motor movement

Inability to judge distance and performing rapid movements

staggering and tendency toward falling

Weak muscles

Slurred speech

Abnormal eye movement

The Lobes of the Brain For a long time, it has been obvious to humans that our bodies and being are divided, that we have a physical body and a non-physical mind. However, modern science and especially the field of neuropsychology and brain-science deny that. Today it is apparent that our thoughts, perceptions and feelings are linked to physical parts of the body, mostly located in the brain. The brain is divided up into four lobes, which are going to be brought up in this paper.

The Frontal Lobe

The frontal lobe is the part of the brain which concerns human behavior. The left frontal lobe has a greater role in language related movements, such as speech, and the right frontal lobe mainly concerns the nonverbal movements, such as facial expressions. It executes movements based on information provided through projections of time and place, and relevant sensory and mnemonic information from other parts of the brain. When viewing functional zones of the lobes there are three types of perspectives one can view the brain from; the lateral view, the medial and the ventral view. The medial view is a cross section of the brain and the lateral view is viewing the brain from below. The picture below is of the lateral view of the brain.

The frontal lobe is divided into three general categories; the motor, the premotor and the prefrontal areas. To best explain the function of the frontal lobe one has to look in to these several separate regions and their functional zones.

The Motor Cortex The Motor Cortex works as a mechanism for movements in different regions of the body. It makes projections to the spinal motor neurons to control digit movements as well as limb, hand and foot. It also makes projections to the cranial-nerve motor neurons to control one’s facial movements. The motor cortex base movements on internal signals, and “suggests” these movements to the premotor cortex which selects them.

A picture of the functional zones of the frontal lobe.


The Premotor Cortex The Premotor Cortex also influence and regulates the execution of limb movement, directly through corticospinal projections, or indirectly through projections to the motor cortex. The motor cortex as mentioned executes movements based on internal signals, as the premotor cortex executes movements based on external signals. The Frontal Eye Fields The Frontal Eye Fields send and receive projections from regions controlling eye movements. Just as the motor cortex and the premotor cortex it executes movements based on internal and external cues, which allows us to both concentrate our eye focus on one specific area as well as gaze around large areas at the time.

The Prefrontal Cortex The Prefrontal Cortex receives projections from the dorsomedial nucleus in the thalamus. It is responsible for controlling the cognitive processes of the movements which the motor cortex has made and the premotor cortex has selected to execute. This means that the prefrontal cortex controls when the movements shall be executed, considering the time and place. It allows movements at the correct timing based on either internalized information or external cues, such as context or self-knowledge. To summarize, one can say that they are all connected; the motor cortex is responsible for making movements whilst the premotor cortex selects these movements and the prefrontal cortex controls the cognitive processes of the movements chosen to be executed.

The Parietal Lobe

The parietal lobe is located on the top-central part of the brain, behind the large frontal lobe. Its name derives from the latin word “paries”, which means wall, and refers to the parietal bone, which is located right above the lobe itself. Surrounding the parietal lobe are multiple sulci (The different fissures, or landmarks of the brain), separating the lobe from other parts of the brain. Function The parietal lobe is mainly responsible for processing information transferred to it by the nervous system. The information processed is tactile sensory information such as pain, touch and pressure. This is mainly done in the so called somatosensory complex, which is very important when it comes to processing the body’s senses. The parietal lobe is also one of the places where visuospatial processing occurs, as well as the knowledge of mathematics, numbers and their relations. Thanks to the parietal lobe, we are able to locate where things are and partly how they occur. Consequences one may face if the parietal lobe is damaged could be difficulties to control eye gaze, difficulties with visuospatial processing (Such as difficulties perceiving the left side of your body and objects in general), and difficulties with language and problems with verbal memory. Interestingly enough, several studies have shown that problems with the parietal lobe may be associated with schizophrenia.


The Occipital Lobe

The occipital lobe handles our vision in various ways. It is a part of the brain which is more difficult to clearly define and separate from the other lobes, but its general functions cover color perception and visual search and recognition. There are no clear landmarks between the occipital cortex and the temporal or parietal cortex on the lateral surface of the hemisphere. In the visual cortex of the occipital lobe there are however three clear landmarks - the cuneate gyrus, calcarine sulcus and the collateral sulcus. The visual cortex is highly laminated in a complex organization. Some areas control the complete visual field, while others only have a lower or an upper visual field. The upper and lower fields of the visual cortex have different functions; the upper field is specializes more on visual search whilst the lower half handles visuomotor guidance. The outer “layer” of the occipital cortex, V1 on the picture, has “blobs” which are separated by interblob regions. In the blobs there are cells which take part in one’s color perception, in the interblobs the cells have a role in one’s form and motion perception. This part of the human brain is responsible for detecting motion, creating vision depth and position.

The Temporal Lobe

The temporal lobe is located in the bottom part of the brain, underneath the lateral fissure. Its name derives from its importance when it comes to memories, or temporal information, as in time.

Function

The temporal lobe is the location of the primary auditory cortex, which is vital when it comes to interpreting sounds and comprehending language. Also, as mentioned earlier, this part of of the brain is heavily associated with the formation of memories. This is much due to the hippocampus which is located in the temporal lobe. The main task of the hippocampus can be described as converting short-term memories into long-term memories. The temporal lobe does also play an important role when it comes to processing visual sensory input and producing emotional responses and reactions. As it contains the hippocampus, damage to the temporal lobe may result


in problems forming memories. In more severe cases this may lead to temporal or permanent amnesia. Also, damage to the lobe may result in problems comprehending sounds and language. Worth mentioning is also the alterations in personality and behavior which may occur if the lobe is subjected to lesions caused by e.g. trauma or epilepsy.

Limbic System the emotional brain

The Limbic System is the area of the brain that regulates emotion and memory. It directly connects the lower and higher brain functions. It influences emotions, motivation, mood, and sensations of pain and pleasure. The Limbic System is comprised of the following parts:

Cyngulate Gyrus It is part of the cerebrum grey matter surrounding the inner Limbic System. It serves as a conduit of messages to and from the inner Limbic System.

Diencephalon

This is a part of the forebrain, but it is counted as a part of the limbic system. It contains two parts;

Thalamus (The Inner Room) The gateway to the cerebral cortex, it is involved in sensory perception and movement with other parts of the brain and spinal chord that also play a role in this. Nearly all sensory inputs pass through it to the higher levels of the brain.

Hypothalamus The hypothalamus sits under the thalamus at the top of the brainstem. It may be very small, but it is very important. It controls autonomic nervous system center for emotional response and behavior, regulates body temperature and many more vital functions. Fun fact: It is shaded blue. The following two play an important role in memory:

Amygdala It decides where memories should be stored in the brain, it is also impportant in making associations. It seems to be responsible for the influence of emotional states on sensory inputs and face recognition.

Hippocampus It sends memories to the appropriate part of the cerebral hemisphere for long-term storage and takes them back when needed. This means that it transferrs memories from long-term to short-term memory. The Basal Ganglia is also a part of the Limbic system, but it is so important that it is turned into its own topic.


The Basal Ganglia A necessity for learning

The basal ganglia consist of a collection of nuclei, outside and above the limbic system. Basically, the basal ganglia receive information from the cerebral cortex and after processing this information the basal ganglia nuclei send the information back. Recent studies on Bengalese finches have shown that the basal ganglia plays a large role in “skill learning” and that it is what makes it possible for us to learn by trial and error. When the anterior forebrain pathway (AFP), a cortical-basal circuit (a circuit which moves from the cortex to the basal ganglia) was blocked on the Bengalese finches, while they were learning how to sing, it completely prevented learning and improvement. This led scientists to draw the conclusion that the basal ganglia circuits are capable of “monitor*ing+ the consequences of behavioural variation produced by other brain regions and /…/ direct*ing+ those brain regions to implement more successful behaviours”. In other words, this means that the basal ganglia can “correct” or “improve” the way our brain works in order to make our behaviour more successful.

Moreover, there are many nuclei in the basal ganglia which have other distinct functions. The largest group of nuclei in the basal ganglia is called the corpus striatum and it consists of many important nuclei, such as the caudate nucleus, the putamen and the globus pallidus. The caudate nucleus sends messages to the frontal lobe and it is believed that these messages are responsible for informing us, in the event of something being wrong, that we need to act and do something. The putamen is believed to help us coordinate automatic behaviours, such as walking or riding a bike. Lastly, the globus pallidus is a nuclei located inside the putamen. It receives messages from the caudate nucleus and the putamen and this information is then sent to the substantia nigra, which is a nucleus located in the basal ganglia outside of the corpus striatum. The substantia nigra is known, amongst other things, to control eye movements.

Neurotransmitters The messengers of the brain

Neurotransmitters are chemicals which send signals from one neuron to another across synapses. There are two kinds of neurotransmitters, excitatory and inhibitory. Excitatory neurotransmitters are neurotransmitters that stimulate the brain, whereas inhibitory neurotransmitters balance mood by stopping brain stimulation. Some of the most important inhibitory neurotransmitters are serotonin, GABA and endorphin. Serotonin is related to emotions and mood. It can block excessive excitatory neurotransmitters firing (i.e. sending signals to other neurons) in the brain and thereby stabilize mood swings. GABA is responsible for blocking excitatory neurotransmitters that lead to anxiety, and it is often referred to as “nature’s Valium-like substance”. Endorphin, which is short for "endogenous morphine", is involved in pain reduction and pleasure. Some of the most important excitatory neurotransmitters are acetylcholine, norepinephrine and glutamate. Acetylcholine has a long list of functions. It works in sensory neurons and in the autonomic nervous system (the part of the nervous system that regulates the function of our internal organs), stimulates our muscles and has a part in scheduling REM, or dream, sleep. Norepinephrine is responsible for stimulatory processes in the body, and is strongly associated with bringing our nervous system to “high alert”, by increasing our heart rate and blood pleasure.


It is released into the blood stream together with its close relative adrenalin, when we need to be on our guard. Glutamate is the most common neurotransmitter in the central nervous system and is especially important for our ability to memorize. Lastly, there is an important neurotransmitter that is both considered to be an inhibitory and excitatory neurotransmitter, and that is dopamine. Dopamine can block the tendency of neurons to fire and it also works to control feelings such as depression. Dopamine can help against depression since it is strongly connected to reward mechanisms in the brain. Some drugs, like cocaine and alcohol, elevate the level of dopamine in our brain, making us feel good. Dopamine is also connected to our ability to focus; low or high levels of dopamine will give us a hard time focusing and can be a cause for daydreaming. Dopamine is also responsible for motivation, or our desire to complete things.

Neural Networks Neural network as a term was initially used when referring to a network or circuit of biological neurons. However, the usage of the term has changed with time, and now it often refers to artificial neural networks, composed by artificial neurons or nodes. Our brains are made up of about 100 billion tiny units called neurons. Each of these neurons is connected to thousands of other neurons and they communicate via electrochemical signals. The signals coming into the neurons are received by the use of synapses. These synapses are located at the end of branches of the neuron cell called dendrites. The neurons receive information from these inputs continuously. In simple terms one can say that the neuron sums up the inputs and if the end result is greater than the threshold value, the neuron fires. This generates a voltage and outputs a signal along an axon. Neural networks are made up of many artificial neurons. Artificial neurons are simply electronically modeled biological neurons. How many neurons that are used depend on the task the neuron has at hand. Artificial intelligence and cognitive modeling try to simulate properties of biological neural networks. The former aims towards solving particular tasks while the latter has a main focus to build mathematical models of biological neural systems.

Documents

Neuropsychology: Anatomy of the Brain · 2013. 2. 14. · Neuropsychology: Anatomy of the Brain Neuropsychology seeks to understand the functions of different parts of the brain,