When Stroke Affects the Parietal Lobe
The parietal lobe is one of four lobes that make up the cerebral cortex, the wrinkly hemispheres of the brain right beneath the skull. It occupies a position at the top of the brain, behind the frontal lobe, a little more than halfway back, extending to the occipital lobe at the back of the skull, and above the temporal lobe. Its blood supply is primarily from the middle cerebral artery, though it does get some blood from the anterior cerebral artery.
The parietal lobe helps us make sense of sensory information, like where our bodies and body parts are in space, our sense of touch, and the part of our vision that deals with the location of objects. This spatial awareness makes it possible to make decisions, plan and navigate the world. Much of the major sensory inputs from the skin (touch, temperature and pain receptors), relay through the thalamus to the PL.
The PL has two lobes, one in each hemisphere of the brain and about the size of a fist. Each side has different functions based on which side of the brain is dominant. According to Erica Camargo, a neurologist at Massachusetts General Hospital and instructor of neurology at Harvard Medical School, most people are left-language hemisphere dominant.
Dr. Rachna Malhotra
“Everyone has a language-dominant hemisphere,” said physiatrist Rachna Malhotra, medical director of the Stroke Recovery Program at MedStar National Rehabilitation Hospital and assistant professor of Clinical Rehabilitation Medicine at Georgetown University. “The vast majority of people are left-language dominant. So, in a parietal stroke, if it hits the left side of the brain, you can have aphasia. Where exactly the stroke hits determines what kind of aphasia there is. If it hits the right side of the brain, the non-dominant side, deficits will be more cognition, thinking, calculation.”
Some of the fibers that span the frontal lobe and temporal lobe run through the PL. “Patients who have parietal lobe dysfunction in the dominant hemisphere on the left, for example, may have difficulty with certain types of verbal expression,” Camargo said. “If there’s an injury close to the temporal lobe, they can have difficulty understanding language. If the stroke is close to the frontal lobe, they can have problems with planning their speech. They may have difficulty repeating words that are spoken to them.”
Dr. Erica Camargo
While a PL stroke can affect language, it can also impact the sense of touch and movement. “When I think parietal lobe, the first things that come to my mind are perception and sensation,” Malhotra said.
A stroke in certain areas of the nondominant hemisphere may produce problems with perception on the opposite side of the body. “Patients will have difficulty with sensation to light touch, to temperature, to pinprick, to pain,” Camargo said. “Sometimes, when that problem affects the right side of the brain, which is important for visuospatial orientation, the patients not only lose the capacity for those sensations, but they may also lose spatial awareness of what’s happening on the other side of the body, on the left side of the body. Some patients can’t really tell what’s in their hand or what they’re holding, or they can’t recognize texture or weight.”
This lack of spatial awareness is the classic stroke deficit often referred to as “neglect.” “Neglect is one of the most important impairments from a parietal lobe stroke in the non-dominant hemisphere,” Camargo said. “That’s the neurological sign we show to medical students over and over — spatial neglect and anosognosia, when survivors don’t even recognize that they have a problem. That is classic for parietal lobe dysfunction: the fact that the patient has absolutely no concept that they had a stroke.”
Camargo gives an example: “You ask a patient if their arm is weak, and they look at their arm. First of all, they may not even recognize that that arm is theirs. But if they do recognize it, they may not recognize that there’s any problem to begin with. That’s a type of neglect, lack of awareness of their neurological deficit.”
The PL plays an important role in awareness and understanding the world on the opposite side of the body, which can manifest in different ways. Sensory neglect — touch and temperature perception — is one of those. Camargo gives another example: “Say I’m stroking both arms of a parietal lobe stroke survivor at the same time with their eyes closed; they may not recognize that I’m stroking both arms simultaneously. When I individually stroke one arm or the other, they’ll recognize that I’m stroking each arm. But when you have stimuli coming at the same time from both sides of the body, they really won’t pay attention to the side that has a problem.”
The PL has close connections with the occipital lobe, which controls vision. “Patients who have injury near the occipital lobe may have hemi-spatial or visual neglect on the opposite side,” Camargo said. “If you only stimulate each visual field separately, they can see. But when you stimulate both visual fields simultaneously, they won’t pay attention to one of the sides. That can present a big problem in therapy because patients may not pay much attention to one side of space during therapy and will need to be encouraged to pay attention to that side often during therapy.”
The ability to know where our body parts are in space is called proprioception. After a stroke in the PL, a survivor’s proprioception may not function properly. “For instance, when a survivor is trying to walk in therapy, they may be unable to tell where their leg is in space,” Malhotra said. “They know it’s weak, they know it’s there, but they don’t know where it is.”
Camargo offers another example: “If the patient has a stroke on the right parietal lobe, and we move their left hand or a finger up and down, they may not be able to perceive that it’s moving or in which direction it is moving.”
Malhotra points out that there is a variety of therapy for a proprioception deficit. Malhotra addresses it with general, overall therapy, and she has had some success with aquatic therapy.
Some PL stroke survivors can have involuntary movements of the arm. “Because they don’t really have much awareness of where the arm is in space, the arm can, by itself, position itself upwards or downwards or in a place where it shouldn’t be going,” Camargo said.
The dominant hemisphere PL plays a role in executive function, which involves the ability to think abstractly, see consequences and make decisions based on that analysis rather than in response to emotion. This is mainly because of the connections between the PL and frontal lobe, which is the primary controller of executive functions. “For instance, if you have a parietal lobe dysfunction on the dominant hemisphere, the sensory input sent to your dominant hemisphere frontal lobe to do a certain type of movement is not received,” Camargo said. “So, the frontal lobe can’t plan that movement accurately, and there is the appearance of an executive dysfunction. That’s what we call an apraxia, when you have an impairment executing planned movements, which often require the integration of sequential movements.”
Neither doctor considered the PL stroke as causing emotional disturbances, primarily because it is not specifically related to the limbic system. However, Camargo pointed out that it can contribute to delirium.
“Delirium is the condition in which, under certain circumstances of brain stress or bodily stress — be that from neurological damage to the brain or infections to the body (the more common scenarios in which we see delirium) — patients are more susceptible to states of confusion. This is more common in elderly patients because older brains may be more fragile and a little bit more atrophied,” Camargo said. “When patients have parietal lobe dysfunction, especially on the non-dominant hemisphere, usually the right hemisphere, that can be very confusing. Not to recognize the left side of the world and losing all their sensory information that they usually receive from the opposite side of the body can be very confusing for these patients, which can be distressing and emotional.”
Stroke in the dominant hemisphere (usually the left) of the PL near the boundary with the temporal lobe can result in Gerstmann syndrome, in which the following problems coincide: “That kind of a stroke can give you weakness, but it also can give you a combination of left-right confusion; difficulty writing, which is called agraphia; difficulty with calculation (acalculia); difficulty with language (aphasia); and difficulty with recognition, which is called agnosia,” Malhotra said.
Depression is common with PL stroke survivors, but no more, or less, common than survivors of strokes in other areas of the brain. “Any type of stroke is such a life-changing event — having to start over as in relearning how to walk, how to bathe and dress yourself, how to communicate. There are plenty of emotional challenges,” Malhotra said. “It’s a very important topic that we really discuss with our patients. We sometimes offer treatment, medical treatment as well as having neuropsychologists onboard who have sessions with our patients as well.”
Therapy & neuroplasticity
In rehab, Malhotra, a physiatrist, prefers to use all three therapies — occupational, physical and speech — in working with PL stroke patients. “Our approach overall is to focus on mobility and function with physical therapy; on activities of daily living with occupational therapy; and language and cognition with speech therapy,” she said. “I am a big proponent of a wide variety of approaches. So, we try constraint-induced therapy. We have a zero-gravity machine that helps with ambulation. Contrast baths to help with sensation changes. Whatever works is how we feel in the rehab world.”
Like other lobes, the PL has the capacity for the unaffected side to take over some functions of the affected side. “That’s the theory behind neuroplasticity,” Camargo said. “That if you have damage to a certain area of the brain, the brain tissue surrounding it or on the opposite side, and the connections they make, can try to help perform functions that were done by the area of the brain that is injured.”
That is the idea behind constraint-induced therapy. “So, we inhibit the unaffected side to see if there can be improvement on the affected side,” Malhotra said.
“I would say that if the patient with parietal lobe dysfunction doesn’t have prominent neglect, the potential for physical recovery is probably better than that of other areas of the brain,” Camargo said. “For example, a frontal lobe stroke causing weakness of the arm or leg so that you really can’t move it — that can be very limiting. But when loss of sensation is your problem, it may not be that limiting because you can still move the arm or leg. Therefore, you can do certain things, obviously not with the same dexterity as before, but it may be less limiting. However, for patients who have neglect, the situation may be worse because it may be difficult for them to participate in rehab, since they struggle with knowing what’s going on in the opposite side of their body or attending to the world on the affected side of their body.”
“I think it’s important that patients who have parietal lobe dysfunction be aware of the type of deficits they have and really engage with their therapists, so they can achieve the best possible recovery,” Camargo said. “And also having the engagement of their family members or caregivers to assist them in their recovery. I think those are really the key to optimal recovery.”
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