What is association cortex

It is rostral to the postcentral gyri, Rolandic fissure, and premotor areas. It has Sylvian fissure as its posterior boundary. It is referred to as prefrontal cortex. Early evidence of the role of prefrontal cortex came from the case of Phineas T. Gage was a foreman on railroad construction in the middle of the 19th century.

The charge unexpectedly exploded as he was packing in the explosive charge. What happened was that the tamping rod blew out of the hole and went through the front of his head, destroying large portions of his prefrontal cortex.

After he recovered physically remarkably only a few weeks , his personality had changed. His actions were impulsive with little regard for consequences.

He became an alcoholic and drifter. Prefrontal lobotomies were performed in the first half of the twentieth century to relieve psychotic symptoms. These have now been replaced with drug therapy. With a unilateral or bilateral prefrontal lobotomy there is a lack of ability remember and relate things over time. Delayed reward has a greater detrimental effect on learning. Attention span and ability to concentrate are greatly diminished.

Abstract reasoning largely disappears. The prefrontal cortex receives massive inputs from the sensory association cortices somatosensory, visual and auditory and also from the dorsomedial nucleus of the thalamus.

Lesions of the dorsomedial nucleus of the thalamus can produce many of the same symptoms as from prefrontal lobotomy.

Prefrontal syndrome or frontal syndrome in patients usually refers to damage of the dorsal superior prefrontal association area. Most research in the dorsal prefrontal area is concentrated within the dorsolateral prefrontal area. This is the area 46 in the above diagram just dorsal to the principal sulcus Figure 9. This is a very important area for many higher-order cognitive abilities. The dorsolateral prefrontal area along with the cingulate cortex are involved in attentional processing, planning, rule learning and memory.

When sequences are being learned, the dorsolateral prefrontal area and the cingulate cortex are highly active. But once learning is complete and automated these areas are no longer active. Many neurons in the dorsolateral prefrontal area and those in the principal sulcus itself i. These neurons receive inputs from a dorsal pathway through the posterior parietal cortex. When occasionally they stop firing during the delay period, this usually signals that the monkey has forgotten the location.

Eye-tracking devices are used to record where the monkey is looking, and the monkey is trained to look towards a particular remembered location. In contrast to the dorsolateral prefrontal area, neurons in the small area 46 in Figure 9. This is a target of the ventral visual pathway through the inferior temporal lobe. The orbitofrontal cortex and the medial prefrontal cortex have direct connections to the amygdala and cingulate cortex of the limbic system and thus provide the emotional component to the planned behavior and memory.

The dominant neurotransmitter in the prefrontal region is dopamine. Dopamine depletion can create lesion like symptoms. Disturbances of the dopaminergic system are thought to contribute to symptoms of schizophrenics and many schizophrenics have hypofunction of the prefrontal cortical regions. Symptoms such as being controlled by alien voices suggest a dysfunction of the executive control system in schizophrenics.

For example, if schizophrenic patients are tested on the Wisconsin Card Sorting Test blood flow to the prefrontal areas is much less than normal individuals. Blood flow to the prefrontal areas is shown to be a functional part of performing this task accurately because when schizophrenics are rewarded for their correct responses blood flow increases much more than it does for normal and they show improved performance.

Further evidence for the close interaction between the prefrontal cortex and cingulate cortex is that neuroimaging of schizophrenics shows impaired activation of the cingulated cortex in cognitive tasks and postmortem histological analysis has shown abnormalities in the cingulated cortex of schizophrenics.

Another way to determine whether or not functions are lateralized to one hemisphere or represented in both hemispheres is to test split-brain patients, patients that have had their corpus callosum transected.

Sectioning the corpus callosum is a last resort treatment of intractable epilepsy. Stimuli can then be input to only one hemisphere without the other being aware of these stimuli. Patients can be tested to see how they process these stimuli.

He can name the object or select an object by touch and pointing. Stimuli are presented to only one hemisphere tachistoscopically. Patients focus on a point straight in the middle of a screen. If the stimulus appears on the left, it goes to the right hemisphere. If the stimulus appears on the right, it goes to the left hemisphere.

So, when the cone stimulus is on the left, is the patient incapable of recognizing the visual stimulus as a cone? Actually, the patient is capable of recognizing the stimulus as a cone. But you have to be clever to show this ability.

The patient can correctly choose, by feel, the correct object. Or the patient can correctly identify it by pointing to it, but only with his left hand. One might say that this is just matching—even cross modality visual to haptic matching—but not language.

But you can convince yourself that this is really language because, if you flash the letters D-O-G to the right hemisphere, patients can pick out the model of a dogonly with their left hands, of course.

Other results from split-brain patients have shown that for most people, the left hemisphere is dominant for mathematics as well as language. Adapted from Sperry, R. Lateral specialization in the surgically separated hemispheres. In: Schmitt, F. The right hemisphere is dominant for music, face recognition, and anything to do with spatial relationships.

For example, even right-handed patients after corpus callosum resectioning split brain are better able to draw with their left hands than with their right hands because it is the right hemisphere that controls the left hand. Thus, the right hemisphere has some functions that are superior to those of the left hemisphere, and the right hemisphere is not just like the left hemisphere without language.

Other examples of superiority of the right hemisphere would be that split-brain patients can fit wooden blocks together of different colors to make a pattern better with their left hands than with their right hands, again showing that the right hemisphere is superior in spatial-perceptual tasks. In conclusion, functions of the brain that are localized to specific brain regions have had considerable clinical importance.

Localization of function can explain why certain syndromes are characteristic of disease in specific brain regions. Nevertheless, no part of the brain works in isolation.

Each and every part of the brain works in concert with every other part. A year old cerebral vascular accident patient was diagnosed as having persistent unilateral spatial agnosia or "visual neglect".

What cerebral region was most likely involved? Lesions of the right posterior parietal visuocortex i. This would be in the right hemisphere for right handers producing left visual neglect. While occasionally lesions of the dominant parietal-occipital hemisphere e. Dominant parietal-occipital cortex. Higher-order integrative cortical areas, called association areas, intervene between the sensory inputs and motor outputs.

Press the labels to see the pathways. Other methods, such as the lesion method, are not as well-known, but still very influential in modern neuroscientific research. Cortical Areas of the Brain : Locations of brain areas historically associated with language processing. Associated cortical regions involved in vision, touch sensation, and non-speech movement are also shown.

The concept of the lesion method is based on the idea of finding a correlation between a specific brain area and an occurring behavior. From experiences and research observations, it can be concluded that damage to part of the brain causes behavioral changes or interferes in performing a specific task. For example, a patient with a lesion in the parietal-temporal-occipital association area has an agraphia, which means he is unable to write although he has no deficits in motor skills.

Consequently, researchers deduce that if structure X is damaged and changes in behavior Y occur, X has a relation to Y. Learning Objectives Describe the association areas of the cerebral cortex. Methods of Brain Function Analysis Behavioral and neuroscientific methods are used to get a better understanding of how our brain influences the way we think, feel, and act.

Key Points Many areas of the brain are required to form a cohesive view of the world and permit perception. The prefrontal association cortex is involved in planning actions and abstract thought. Then the brain makes a decision and sends nerve impulses to the motor areas to generate responses.