Thank you for your question. I will first give a general overview of the function of the parietal association cortex and then go into some of the lesions which may make it easier to understand function. Also keep in mind that the anatomical basis of some of these lesions is not clearly set in stone and there are always reported cases of other regions producing similar disorders.
The term association cortex refers to regions of the cortex which have extensive connections with multiple sensory and motor areas. They combine information to give rise to complex parts of cognition. The parietal association cortex refers to the posterior parietal cortex, the part that does not include the primary somatosensory cortex. This region is anatomically divided into the superior and inferior parietal lobules by the intraparietal sulcus.
The posterior parietal cortex is connected to motor, somatosensory and visual areas of the cortex. It integrates this information to inform movement and give a sense of where the body is in space, and where objects are in relation to each other. These two functions are often interrelated. For example, when reaching for a book on your desk while looking at your computer screen, your brain must know where the book is within your visual field, in relation to the screen and to your hand. The dorsal part of the cortex is predominantly connected to the somatosensory cortex and is more involved in motor function, whereas the ventral parts of the cortex is mainly connected to the dorsal stream of the visual cortex and is more involved in spatial awareness (you can read more about the two-stream hypothesis here).
This is when the patient ignores events in the half of space that is contralateral to the lesion. They are usually caused by strokes occluding the middle cerebral artery, affecting the ventral aspect of the parietal lobe (referred to as the inferior parietal lobule). Patients can even neglect shaving one half of their face, and when asked to draw objects, it is only half complete.
Hemispatial neglect usually occurs from a lesion on the right side of the brain. It is thought that the right parietal lobe is dominant in processing spatial information from both sides of the body. So when there is a lesion on the right side, the left side is not able to compensate. Note that lesions in the frontal cortex and superior temporal gyrus have also been implicated in this condition.
A similar condition is asomatognosia where a patient ignores the existence of their arm or leg on the opposite side of the lesion. This impacts the sense of self, rather than the awareness of objects in space.
Damage to more dorsal parts of the posterior parietal cortex, usually on the left side can cause apraxia, which refers to an inability to perform actions even though the muscles required are perfectly normal. There are many types of apraxia depending on the exact region affected. Ideomotor apraxia is characterised by an inability to perform hand gestures such as waving goodbye and acting out movements such as pretending to brush their teeth.
Acalculia and agraphia
The posterior parietal cortex is also involved in abstract thinking. Acalculia refers to a difficulty performing calculations, especially with multi-digit numbers. Lesions in the left angular gyrus can cause agraphia and alexia, where patients cannot read, write or spell. These functions depend on the ability to remember the sequence of letters in a word, or the place value of digits which is a form of spatial awareness.
This deficit reflects the importance of the posterior parietal cortex in combining visual and motor information to guide movement. Patients with optic ataxia are unable to reach for an object in their visual field. They can however reach when visual information is not required, such as reaching their leg in the dark.
Essentially, the parietal association area serves multiple functions, with a predominant involvement in spatial awareness. I hope this answered your question and let us know if you require further clarification.
If the posterior parietal cortex is responsible for giving a sense of where the body is in space, then how is it that a patients with optic ataxia are able to reach for their leg in the dark? How would they know where their leg is?
There is great variation in the types of deficits seen in these patients but generally they have greater trouble reaching for objects in the peripheral parts of their visual field. The classical understanding is that this impairment causes difficulties in movements guided by vision. It is also usually part of a condition known as Bálint's syndrome which includes other deficits. You can get optic ataxia just by itself (even rarer than Bálint's syndrome) and interestingly these are caused by lesions in the superior parietal lobe or the intraparietal sulcus. There is a specific area in the macaque brain around that area called the parietal reach region which produces optic ataxia, but in humans they aren't entirely sure whether there is only one parietal reach region, so I would not worry too much about the localisation. This also is against what I said earlier about the more dorsal parts of the parietal cortex dealing with somatosensory information and ventral parts visual, but you must keep in mind that it is not as simple as drawing clear boundaries to dedicate to function and many exceptions exist, especially within these association areas.
Specifically in terms of your question, it really depends on the extent of damage. The function you are referring to is proprioception, which is essentially knowing where your body is in space. Now it was thought before that proprioception was not particularly impacted in optic ataxia since it is due to a deficit in combining vision with movement. Proprioception on the other hand relies more on the function of the cerebellum and cortical areas, rather than sight. This is why the patients can usually touch their knee when asked without relying on vision. Recently however, it was seen that it may in fact be much more complex than this and optic ataxia may impact proprioception, and indeed with more severe lesions they cannot do the pointing to their knee in the dark. I would not worry too much about the exact lesion and the variations but instead have this in mind to understand the function of the parietal cortex a bit better. There is very little known about optic ataxia since it is very rare so something like hemispatial neglect is much better to focus on since some more detail exists on it, though again it is still not that well understood.
I hope this was helpful and let us know if you have any more questions.
Stunning site! Do you have any accommodating clues for trying essayists? I’m wanting to begin my own site soon yet I’m somewhat lost on everything. Would you prompt beginning with a free stage like or go for a paid alternative? There are such a large number of Eye Of The Tiger Leather Jacket out there that I’m totally overpowered .. Any thoughts? Welcome it!
This is truly an practical and pleasant information for all. Thanks for sharing this to us and more power Leptitox
I curious more interest in some of them hope you will give more information on this topics in your next articles. Leptitox Review
We are really grateful for your blog post. You will find a lot of approaches after visiting your post. Great work Leptitox
Excellent effort to make this blog more wonderful and attractive. Leptitox
Really decent post. I just discovered your blog and wished to say that I have truly cherished surfing around your blog entries. Regardless I'll be subscribing for your nourish and I trust you compose afresh soon! LeptoConnect Reviews
I am extremely delighted in for this blog. Its a useful theme. It help me particularly to take care of a few issues. Its chance are so awesome and working style so fast.survival tips blog
I concur with your blog and i will have returned to check it more later on so please keep up your work. michael kors outleti cherish your substance and the way that you compose piano for all reviews
I just found this blog and have high hopes for it to continue. Keep up the great work, its hard to find good ones. I have added to my favorites. Thank You. Cinderella Solution
I was completely pursuing down. Grateful for such post and please keep it up Great data.I like all your post. I will continue taking off to this online journal once in a whilewww.vert-shock.org/
A great website with interesting and unique material what else would you need. Cinderella Solution
This website and I conceive this internet site is really informative ! Keep on putting up! Leptitox
This website and I conceive this internet site is really informative ! Keep on putting up! The Underdog Advantage
I really adore effectively looking through your total online journals and discussions.
I think this is an enlightening post and it is extremely helpful and educated. in this way, I might want to thank you for the endeavors you have made in composing this article.Ultimate Herpes Protocol
To start with You got an incredible blog .I will be occupied with more comparable points. i see you got truly extremely helpful points, i will be continually checking your blog much appreciated. EZ Battery Reconditioning Review
This is a great article thanks for sharing this informative information. I will visit your blog regularly for some latest post. I will visit your blog regularly for Some latest post. His Secret Obsession
This is exceptionally intriguing substance! I have completely appreciated perusing your focuses and have arrived at the conclusion that you are ideal about a considerable lot of them. You are extraordinary. NooCube Reviews
Unfathomable posting this is from you. I am truly and genuinely excited to peruse this radiant post. You've truly awed me today. I trust you'll keep on doing so! The Lost Book of Herbal Remedies
This will be the appropriate weblog for everyone who wants to discover this topic. You are aware of a whole lot its almost difficult to argue to you (not too I really would want…HaHa). You certainly put a different spin on the topic thats been discussed for some time. Great stuff, just wonderful! Best Testosterone Booster
This is truly an practical and pleasant information for all. Thanks for sharing this to us and more power Baby Sleep Miracle
Do you mind refreshing your blog entry with extra understanding? It ought to be truly valuable for every one of us. His Secret Obsession Reviews
I have as of late begun a blog, the information you give on this webpage has helped me enormously. Thanks for the majority of your chance and work. The Lost Ways 2 Review at Eubookshop.com
What a really awesome post this is. Truly, one of the best posts I've ever witnessed to see in my whole life. Wow, just keep it up. Text Chemistry
This is a great article thanks for sharing this informative information. I will visit your blog regularly for some latest post. I will visit your blog regularly for Some latest post. Relationship Rewrite Method
What a truly amazing post this is. Really, outstanding amongst other presents I've ever seen on find in as long as I can remember. Amazing, simply keep it up Ultimate Herpes Protocol
Much thanks for composing such an intriguing article on this point. This has truly made me think and I plan to peruse more Hero Instinct
Congrats for making it effectively! you are presently enjoying the product of your hard works and works of your concentration and commitments.survival guide blog information
Superb showed data. I thank you about that. Almost certainly it will be exceptionally helpful for my future ventures. Might want to see some different posts on a similar subject! Pregnancy Miracle
To start with You got an extraordinary blog .I will be keen on more comparative subjects. i see you got truly exceptionally valuable themes , i will be continually checking your blog much obliged. Easy Cellar
I am genuinely thankful to the holder of this web page who has shared this wonderful paragraph at at this place Custom Keto Diet
cool you write, the information is very good and interesting, I'll give you a link to my site. Resurge Supplement
Thank you for the post. I will definitely comeback. Resurge
Great tips and very easy to understand. This will definitely be very useful for me when I get a chance to start my blog. Resurge Review
i am for the first time here. I found this board and I in finding It truly helpful & it helped me out a lot. I hope to present something back and help others such as you helped me. Resurge Supplement