Association cortices

In the brain we have primary areas (motor area, somatosensory area, auditory area, olfaction, taste and visual area) these areas are known as specific areas. These are make less than 10% of the total area of the brain.

What’s the function of the remaining area of the brain? Why do we call it association area?

We talked previously about phrenology, this tendency to assign specific functions to parts of the brain. It happens that phrenology is a kind of ………. because we cannot look to the skull and tell this person is smart or aggressive this is really anti-science by definition.

Between the 2 tendencies, first tendency that was empirical and another extreme tendency claiming that all areas in the brain are equivalent and can do everything. (this theory was predominant in the 19th century until an incident happened and was published about a patient (brocca’s patient) who last the ability to communicate in spoken words and after his death they made an autopsy and they found that an area of his brain is missing and since that time this area was labeled brocca’s area.

From this clinical observation, neuroscientist started to admit the idea that silent or association areas can play a major role in organizing the integrated information and organizing the so called higher functions of the brain.

When we look here based on more model approach and some research work on human (but mostly on experiments performed on animals and specifically on primates) we know nowadays that we have primary areas and in the neighboring there is unimodal association areas. For example we have motor and premotor areas, we have somatosensory area and in the neighborhood primary association area associated to this area, so on for vision and audition.

Then we have a transition to the major association areas (core association area) that make the largest part of the human brain. (yellow area)

What is the design of the function of these association areas?

we have superior longitudinal bundle and an inferior longitudinal bundle. One associating visual to frontal and one associating prefrontal to temporal and vision. These areas, major areas, multimodal association areas are involved in the integration of information coming from everywhere (not from one modalitity). And whenever u say not from one modality also space and time factors can intervene. We have integration of information not by association visual auditory or tactil also by comparing the actual sensation to a past experience. Here another dimension will intervene, we have the present with multisensory input in addition to this vertical dimension that means time, memory and learning. So these areas are involved in the integration of information to give a final answer, perception, idea or solution.

If we want to make an extremely simplified diagram of the work of these areas, we start by a unimodel sensory input a visual or tactile or olfactory input. We start by one modality, this modality will go to a higher order sensory cortex but still unimodal in the same area. Then it will

be transferred to the association areas, these association areas can be limbic or can be the remaining which is multisosnsory perceived and from all of these, all the information will be transferred to the prefrontal cortex. The prefrontal cortex will feed info the premotor cortex, supplementary motor cortex then going to the motor cortex. Here we have the final end result of the processing of all the info.

Here is not only simple motricity like walking also writing speaking, designing, playing music, every single higher fct in our brain will be expressed ultimately through the output of the cerebral cortex.

Let’s start with the prefrontal cortex because this is the area where the end result of all info will come here. Look here im taking only mammalians look at the prefrontal lobe the human brain and the scull are characterized by frontalization. The frontal lobe make 1/3 of the total area of the brain. Why do we have this important prefrontal lobe? We have dorsolateral and inferior part of it. In the end of the inferior part we have the orbitofrontal that make a kind of a bridge between conscious somatic and limbic fcts, The interface between voluntary perceived somatic association areas and going to the limbic fct.

Most of our work is performed on nonhuman.

For example for this monkey, we see here the lateral and ventral inferior views of his prefrontal area. We have a dorsolateral convexity and an inferior prefrontal convexity separated by the principle sulcus. And we have the orbito-frontal cortex.

Working on a monkey we have some tests. In this test here we have 2 containers, we put in one of them food pellet then we close on the mokey for certain time. So this is a delay task test. After few seconds or minutes u open the screen and the monkey is allowed to search for the food. After one or two trainings the monkey will be able to find the food without any error. Why? Because he can conserve in his brain for a certain time a memory, he can learn that food pellet was hidden here and he can get it. This is delay, you have only time.

On the other side u have time and space. Look how can w asses these.

Here we have 2 containers one of them is labeled, the exepiment hides the food pellet in the labeled container then close the screen and change the position of the container and after a while we have a delay in time and also to remember the place and the monkey can succed in doing that.

How can we explain that?

If we put a microelectrode in the dorsal convexity of the brain of this monkey to record the activity of some samples, we can see in the recording of the first trial the neurons have a very small firing before the delay(during the cue) but during the delay the neurons are firing all the time. In the 2nd trial the basal firing of neurons continue to be a little bit higher. In trial nb 4 we can conclude that the firing of this neuron is related to memory formation, the neuron continue to fire for seconds and minutes to keep it raise and to allow the animal to find back what is interesting to him to accomplish a task. So in able to accomplish a task u need to integrate

many info(visual info to store it somewhere and after a while to be able to recall this info and to do the task and coordinate different mvt). This a first indication that in this area we have cells that are related to memory formation.

This another example in training a monkey

We put an object in the corner of the screen we can see that when the monkey start tho stare the activity of the neurons where not very high when the target disappears there is imp firing, in the brain of the monkey there is sthg firing in response to the past experience. Now if the monkey is allowed to move his eyes instead of fixing them, cell firing will disappears. This mean that we have in the superior convexity neurons that function in correlating visual cues to make a kind of memory to these cues and to coordinate, to be involved in putting strategies to achieve a goal or task. This the so called coordinated and adjusted behavior. In all of our behavior we put a plan and this plan is based on multisensory info coming and memory plus taking into consideration the space. So we can plan our trajectory, our tricks, and our works. So it seems that the dorsal superior prefrontal convexity is extremely important in all of these scenarios. This is area is very important for putting strategies in playing chest.

Doing these experiments in the monkey if we produce a small electrical stimulation in this area through the microelectrode the performance of the monkey will improve. If we inject in this area a dopaminergic antagonist (we have mesostriatum mesolimbic and mesocortical) the dopaminergic neurons send an important supply to this area. So if we inject dopaminergic antagonist by injecting 5-hydroxydopamine, the monkey will never be able to accomplish any task. All the performance will become random.

If we destroy the area of the principle sulcus, the monkey will fail to do anything. So this area contain neurons that are involved in planning behavior according to time and space and using multisensory input and past experience and learning.

In the area of inferior convexity doing the same experiment on the monkey, if we destroy this area the monkey will not be able to do any task with or without delay, changing space or without changing space. So as a final conclusion, this area is an extremely important area although it seems to be a silent area in our brain it is an extremely important area for humans to navigate in space and time and to coordinate all of their activity in space and time and to adjust to anything that can happen in their environment.

Final example about this area, in a functional recording (based on blood flow) of the brain at rest of a normal volunteer and a schizophrenic patient, we can see the difference between them, (yellow mean the activity red is the max) at rest for the schizophrenic patient didn’t have any activity in this region( in contrast to normal person) but he has hallucination ( activity in the visual area) his not in contact with the reality.

For the orbito-frontal area it’s an interface between the conscious behavior, planning, memory, learning and all kind of internal regulations.

We have limbic association areas in the orbito-frontal and temporal lobes, in the temporal lobe we have essentially memory.

Let’s talk about the orbito-frontal lobe it’s for planning and emotional behavior. remember this important input,in this nucleus more than 1/3 of our talents are made by the medial groove and this medial groove is connected to the prefrontal lobe.

How can we know about it?

This is the case of a worker used to be foreman of a company, this foreman injure his brain by an explosion. Just after the accident he was awake he could talk and communicate with people. After few days when he recovered his performance was not impaired at all (learning, speech ...) but he showed some abnormal behavior, after a while the company dismissed him due to irresponsible behavior. As if that in that area in the brain that does not affect learning there is matching between the individual behavior with the social behavior, ethics, cultures and learning past experience. It means that this area is an extremely important area that can make an interface between our past experience, our culture, our social standards with our internal means like eating, drinking, playing, sexual behavior and matting have to be adjust with the social behavior. Otherwise if u find an eldery that is not adjusted with the environment we can say he’s becoming frontalnoch???

In addition to that social adjustment is related directly to complying with the social behavior and self discipline and to be able to deal with other people. An extreme example of defect in dealing with the environment is aggression.

During a scientific meating in 1960’s a scientinst (jackobson) made demonstration, showed to the society he can tamp a wild animal to become without any sign of aggression by cutting this area of his brain (the cingulated area and part of this frontal area) by cutting this area we ca tamp the animal and remove aggression and by that the animal can adjust with the environment. As that meeting a neurosurgeon was fascinated by the idea and started to this operation on criminals and patients suffering from some diseases. The neurosurgeon at this time claimed that the patient will not lose any fct but is being control. But in reality the patient will become flat, inert without iniative complete change in his personality.

An example that can happens to many people governors and administrators in our environment, someone subjected to this neurosurgery, the simple task can become very difficult. Like playing a roulette we inform the patient that he has to gamble on the shape, and if he picks this shape he will win. He starts gambling and winning money, then the strategy changes and we change the shape but he insist to continue gambling on the old shape and losing money. Despite changing the shape and informing him about the change he continues to pick the old shape. What does it mean that? When we hit this area of the prefrontal lobe we lose some flexibility and some autoregulatory mechanisms as if we are suffering from a kind of cerebral rigidity, so we lose the wisdom of judging and the ability to adjust with the new environment.

Temporal lobe: MemoryWe have the memory corridor, we have based on experimentation on humans and on animal some areas in the inner temporal lobe are based on emotions and fear. We have visual and auditory memory and we have language, most of our knowledge was gained based on a pioneer experiment made by Pantheon. He was doing experiments on awake patients if you do stimulation on the inferior temporal lobe the patients will report to you that he is seeing flashes or a strips of a film. If you go a little bit inside the parahippocampal gyrus the patient will show fear or emotional behavior.As a summing up based on animals and based on humans and pathological cases.1. Inferior temporal: visual learning

A patient having a lesion in the medioventral temporal cortex (The ventral aspect, if you remember the occipito-temporal gyrus separated from the parahipocampal gyrus by the collateral sulcus.) If a patient is having a trouble here and you place in front of him an image he can draw it but cannot identify it. This area is the area for visual identification of visual image thus mainly for facial recognition. Patients having trouble in this area will suffer from “prosopagnosia” they can tell you I have 4 kids and will be able to remember all the details about them (their grades age,….) but he cannot recognize their faces even he cannot evoke their names. This area is for integration of the visual image with a shape or language (spoken or written).2. Superior temporal: Auditory learningThe superior part is for auditory learning. If we have a bilateral temporal lobotomy for some tough cases of temporal epilepsy this suregery will do a complete change in the personality of the patient. This is a cross section of the human brain.

This is taken from a soldier who took a bullet that destroyed the hipocample formation and the amygdalum, the patient will suffer from a Kluver-bucy syndrome. Extreme docility, temptation to put everything in his mouth excessive perverted sexual behavior and difficulties to adjust to the environment. If we do the loboctomy without amygdalum we will lose the ability to acquire new memories. If you impair the hippocampal formation the patient or animal will not be able to make new memory. Learning is making new memory and this happens to elderly patients, they can talk to you about their memory very old memories but they cannot recall something that happened a week ago, because they cannot add to their old memory. The resistance with time to do new learning is due to aging sometimes.This area is important to learning and related to hearing.

Left brain is related to auditory input and to language while the right area is related to listening to music.

This is taken from a schizophrenic patient and a normal patient. The schizophrenic patient has his hippoccampal formation shrunk and the ventricles enlarged. People suffering from schizophrenia, although they tend to start outstanding in their intelligence, but after some time they will become confused and will not be able to retain new memory and adjust to the environment.

For the remaining parieto-visual areas the sensory areas:

Parietal lobe: Higher sensory function & language- Lesion ------ body image- Attention to the spatial aspect of sensory input

- Damage to left: aphasia; agnosia; astereognosia

They are involved in visual, somatosensory and auditory information. We know about cases of dislepcia where patients have a difficulty in associating visual information with somatosensory or auditory…This is based on clinical observation. People having problems in this area will suffer from aphasia, agnosia and astereognosia.

Aphasia (cannot speak properly)

Agnosia: (cannot identify objects properly)

Astereognosia (they cannot identify objects by simple touch).

Also will have: Gerstmann's syndrome 1. confusion left right2. finger agnosia

3. disgraphia4. discalculia

We know about the Grestamann’s syndrome whenever you have an infection in the left hemisphere and related to this pareito-oxcipito-temporal area (angular and the supra marginal gyry and the area of auditory integration: wernick’s area) this will lead to confusion left right, inabitity to identify the opposite part of the body some patients can tell you someone is putting their leg on my leg, I want to remove it and they cannot pinpoint or identify a point in their body, they cannot do accurate drawing due to bad mental calculations.

Damage to right: hemi-neglect of the left side

From people suffering from the right hemisphere, they show the syndrome of hemi-neglect they neglect the opposite (left space).

Here a patient’s drawing first he is completely denying the left side, after 3 months some parts are still missing, after 9 months of treatment he is able to draw full drawing but still some parts are still missing. These patients can wear their jackets on one side and totally neglect the other or even shave one side of face.

Here this shows that we have an area in the brain that is related to spatial representation.

V. Hemispheric AsymmetryWe know that our cerebral hemispheres are not completely symmetrical. Volume wise external grossmodal shape they are the same but they are not symmetrical. How do we assess the asymmetry? We have many tests: Planum temporal, sodium amytal test, tachistoscopy, dichotic auditory task.

A. planum temporale

In one of the patients I will show you by taking the brain like the brains u have in ur lab. you open the lateral fissure and see the gyry of heichel on the superior edge of the lateral fissure behind you see this area here this area is extremely imp on the left area not the right this is related to language (you know in language we have both spoken language and hearing) this area needs both integration between speech and hearing to identify the words if we have a disconnection we could have incoherent speech this can open the way.B. Lateralization of higher functionsThe Na amytal testa. Handedness and speech

To test the language broca’s area in people’s brain. in normal people scientists use a practice they used to inject small injections of amytal in the left or right carotid arteries there is no mixing between blood in the left and right carotid arteries.If you inject amytal in the left carotid artery and you ask the patient to talk aload after few seconds he will stop.If you put 5 times the doze in the right carotid artery he will keep on talking because ammital is hitting through the left carotid area the brocca’s area in left area. This is used to assess the location of brocca’s area in humans.Follow this table

b. Moodleft: depressionright: euphoriaWhen you inject amytal in the left carotid the patient can also get a little bit depressed if you put the same doze through the right carotid patients will become euphorical( mental and emotional condition in

which a person experiences intense feelings of well-being, elation, happiness, excitement, and joy) .some patients that have a stroke in the right hemisphere they are happy they want to go out of the bed and fall down (irresponsible).So even for the mood we have a kind of asymmetry between left and right.

C. Tachistoscopy

If we try this techiscopytest, images coming from ur extreme left visual field will fall on ur nasal retina and will be transmitted to right cerebral hemisphere and vice versa. If u ask a volunteer to name something sitting on the extreme right visual field, he can name it easily, because it will go to the left cerebral hemisphere where we have the language area but if we put the same test in the extreme left visual field he will have difficulties in naming it. If we do a calostomi , cut the corpus collusum, the patient will not be able to name objects sitting in the left visual field. He can identify them (draw them) but he can’t name them because we need corpus collusum (remember the major forceps) this is to transfer the information from right to left. Because the right cerebral hemisphere is mute and left cerebral hemisphere is disconnected from the right.This is also for hearing, right cerebral hemisphere is mute. Language area in most of the population are sitting in the left hemisphere but right cerebral hemisphere is specialized in arts drawings and kinds of shapes patterns hearing music. So we have a kind of asymmetry between left and right. This doesn’t mean dominance. It is a kind of a migration of function to have more space for each function.

An example of this conflict between the right and left cerebrum, this complex was observed in patients having colostomy due to accidents or sever epilepsy. They were subjected to operation of separating their two cerebral hemispheres. We do a mid-sagital cut in the corpus cerebral hemisphere, the patient will have no problems for things in the front but things in the extreme visual field will make problem for him. It is not only for the patient, u see the patient can for something coming from the extreme right visual field, he can indicate it and name it. But something sitting on the extreme left visual field, he can’t name it.

Try to read the colors, can u make it :P!!

You will fail in most of the tests, this is an example of a conflict. Now if u look at it from outside, you will fail totally from the extreme visual field. Here it is in front of you and ur failing. it is not a dominancy, here if I want to give u a final statement this is not left dominating right, this is right dominating left. You can’t read it, u have the color impression dominating your verbal reading. We have at any moment a kind of integration and a division of work between left and right hemisphere. Why do we have this? This does not exist only in human, in birds u know about experiment , there are singing birds they can learn songs.

If u do a destruction of the left hemisphere, the animal will stop singing, after relearning he can go back to singing. If u destroy both hemispheres it will go away. If u do the opposite, u destroy the right cerebral hemisphere, the animal will continue singing , this means that we have lateralization of the capacity. This lateralization of capacity is found in humans but it is not necessarily a given after birth or during embryonic life because new born babies they sometimes tend to show lateralization to left and right and to start speaking. And some of the babies will be left handed while others will be right handed. Don’t try at all to force the baby to use the right hand, it is absolutely wrong. It is shown it is a kind of random distribution between left and right cerebral hemisphere. During critical ages, and after two 3 years , if an accident happens to the baby, the language area and the handiness can shift easily from left to right or from right to left. But these can happen during critical periods during post embryonic development, later on we lose this ability. This is why the mother language is important

So we have distribution of work between the two hemispheres and no dominance.

During early life, we still have this ability and flexibility to shift a function from one side to another. But we can lose this ability after a certain time during early childhood.