Visual association cortex

Siegel RM, Raffi M, Phinney RE, Turner JA, Jando G. 2003. Functional architecture of eye position gain fields in visual association cortex of behaving monkey. J Neurophysiol 90(2) 1279-1294,... 

Afferent nerves carry information from the eyes to the PVA and on to the visual association cortex, whereas efferent nerves send action potentials in the opposite direction. Stored visual memories in the visual associate cortex travel backward to the PVA, evoking a pattern of activity in the topographically mapped areas to produce a perceived image. Because this image originated from memory, it is a perceived mental picture, not a sensation. 

Figure 2. A. Distribution of the serotonin receptor, 5-HT2 subtype which binds the indoleamine hallucinogens, in human temporal cortex as indicated by the binding of radiolabelled ketanserin. While the receptor is relatively sparse in the hippocampal area and entorhinal cortex on the top right, it is concentrated in the temporal association cortex including the area concerned with visual association.

The thalamus is the gateway to cortical processing of all incoming sensory information, represented in Figure 2.1 by the three major systems somatosensory (S), auditory (A), and visual (V). Primary sensory cortices (SI, Al, VI) receive information from the appropriate input modules (sensory organ -I- thalamus). The association cortex integrates information from primary cortices, from subcortical structures, and from brain areas affiliated with memory to create an internal representation of the sensory information. The medial temporal lobe (i.e., hippocampus, amygdala) serves two major... 

Serotonin s effects include classical neuronal inhibition, as well as modulation. The study of dreaming teaches us that disinhibition is likely the cause of positive signs of hallucination, emotional intensification, and confabulation, whereas demodulation more likely causes the negative signs such as memory loss, disorientation, and bizarreness. Serotonin blockade induced disinhibition is one of the mechanisms by which the very same set of aspects of model psychoses is generated the visual distortion and hallucination could result from visual system disinhibition the emotional intensification could result from limbic system disinhibition and confabulation could result from associative cortex disinhibition. 

Johnson DM, Illig KR, Behan M, Haberly LB. 2000. New features of connectivity in piriform cortex visualized by intracellular injection of pyramidal cells suggest that primary olfactory cortex functions like association cortex in other sensory systems. J Neurosci 20 6974-6982. 

Intellectual deficiency, shown by concreteness, lack of abstraction, primitive language and arithmetic skills, poor visuomotor integration and difficulties in praxis is ascribable to cerebral neocortical dysfunction. In very severe cases, frontal release of primitive sucking and grasping reflexes, autistic vacuity and poor visual attention can be attributed to dysfunction of frontal, temporo-limbic, and occipito-parietal cortex respectively. Association cortex functions are impaired more than those of primary analyzers, probably reflecting plasticity of function with limited overall cortical capacity. 

In one subtraction they compared the Fixed task with the Conditional task When selection of a movement in the conditional task was made, significant increases in regional cerebral blood flow were found in the visual association areas of the left superior parietal cortex. Because the fixed task compares to the all task, the subtraction can be written (a44-all). These two tasks differ only in the left superior parietal cortex significantly. The authors think, that the activity of this area is related to the process by which movements are selected and not because the movements were spatial, (see also Roland PE. 1993, pages 249,250)... 

The posterior parietal cortex is located posterior to the somatosensory cortex and serves as its unimodal association area. In addition to further processing of somatosensory input, information from the somatosensory cortex is integrated with visual inputs in this region. Association tracts from both the somatosensory cortex and the visual cortex terminate here. This activity is important for planning complex movements and for hand (prop-rioception)-eye (visual) coordination. 

In SUMMARY, areas of the cerebral cortex can be identified according to the bodily functions which they control. For example, the motor cortex for muscle control, somatosensory cortex for sensory input, visual cortex for visual input, an area concerned with speech, etc. In addition to these specific areas, the cortex also contains highly developed association areas which are probably involved in the complex synthesis of information. 

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