Parietal Lobe Definition

The parietal lobe of the cerebral cortex in both the left and right hemispheres are critical for sensory perception and language processing. Aphasia (disordered speech), tactile agnosia (incapability to differentiate an object by touch), and agraphesthesia are common indications of damage or degeneration of the parietal lobe (difficulty identifying a traced form, number, or letter on the skin).

Parietal Lobe Function

Each dominant brain region and the concerned subregion of the parietal lobe impact the function of the parietal lobe. Dominance allows asymmetrical activities in the brain, which improves motor, language, perceptual, and emotional processing in the parietal lobe. Although right brain hemispheres are dominant in newborn neonates, genetic variables influence which side of the brain is dominant.

Limited asymmetry is linked to neurological illnesses like schizophrenia and bipolar disorder when there is insufficient variance between the functions of either portion of the brain. There are thus no guarantees that what we say regarding parietal lobe operation and also which component of every lobe performs which function is applicable to everyone.

The parietal lobes are exceedingly complicated and are best classified by their location. The parietal lobes’ primary roles are to accept sensory inputs, link these sensations with specific behaviours, and synchronise them with other sensory impulses occurring at the same moment.

There are five functional regions of the parietal lobe. The following are the

• Area of primary reception
• Area of somesthetic connection
• Area for multimodal reception
• Area of granular insularity
• Area for multimodal assimilation

All of these areas are intricately linked to one another and to other central nervous system elements. And besides, the brain does not comprehend information in a single step. The cells and tissues that connect to the parietal lobes, as well as the lobes altogether, are known as the parietal lobes.

They collaborate to allow us to react to a wide range of sensory events. The parietal lobes seem to have a role in how much we react. Studies on aggressive males, for example, have shown numerous brain anomalies such as greater parietal white matter regions and smaller grey matter areas.

In layman’s terms, grey matter contains the brain’s control centres, while white matter supplies millions of interconnected connections. As an example, there are too many linkages and too few control mechanisms in the case of aggressive inclinations. We don’t know exactly how this works. A sliced-through piece of a human brain is shown below, revealing the various grey and white layers.

Parietal Lobe

Primary Receiving Area

The parietal lobe’s major receiving section receives information through our skin, muscles, and joints. It responds to contact, texture, shape, motion, and direction of motion. Every intake region has a distinct histology since distinct types of sensory neurons are present in every input region. These particular clusters of neurons react to skin temperature variations, pain, touch, and other stimuli.

The parietal lobe is in charge of prioritising various inputs based on how much they influence (arouse) us. A stimulus will fade into the background if we hardly respond to it.This is why background music is not always audible and odours fade. And, when you read this, are your shoes or socks perceptible? As you’ve been just reminded, you most likely can now.

You discontinued experiencing them since you stopped listening to them; your parietal lobe recognised that you weren’t reacting as strongly to the touch stimuli as you were to the display and your reading skills, so the touching feeling was pushed towards the back of the line.

It’s fortunate that the parietal lobes organise stimuli depending on our level of arousal; whether they didn’t, we’d experience so numerous sensations at once that it may be almost difficult to operate. Individuals with serious chronic pain cannot concentrate on a reading, entertainment, a good food, community interactions, or any of a range of other pleasurable and unpleasant diversions.

As a result of the parietal lobes’ prioritisation of pain perception, a person is unable to disregard pain sensations that overwhelm the brain. It has been shown that deep breathing techniques, massage, and certain odours alleviate pain. This is partially due to the fact that they redirect attention away from pain signals, leading the parietal lobes to temporarily reduce their priority.

The primary receiving regions of the two parietal lobe halves are separated by Brodmann’s areas 1, 2, 3a, and 3b. Brodmann’s areas are brain regions that vary according to the kinds of cells present. The sequence of Brodmann area (BA) numerals has nothing to do with rank or organisation; it simply indicates the sequence in which every cell cluster was initially recognised.

You won’t be required to know every Brodmann region since they’re becoming less important, particularly as new brain research emerges. Considering the importance of Brodmann’s regions, on the other hand, allows us to get a better understanding of brain function. This holds true for the parietal lobe as well.

BA 3 is the principal tissue type of the parietal lobe’s primary receiving region, which gets the majority of its sensory information from the thalamus. Area 3b processes the electrical signals that enter from nerve terminals on the skin and within the body. Electrical signals (evoked potentials) from neurons that assess the body’s location in space arrive in region 3a (proprioception). BA 3 receives and relays this information.

Regions 1 and 2 receive evoked potentials from BA 3. Area 1 of the Brodmann map is responsible for texture analysis, whereas area 2 is responsible for shape, size, and position processing. For instance, your cat’s head abruptly collides with your elbow. Examples of senses that communicate information to BA 3 include the quality of the hair, the contour of the skin and bones of the skull, the force with which the cat bangs its head, the injured area of skin, and the placement of your elbow. All of these messages are grouped and sent to BA 1 and BA 2.

Groups of stimuli are also processed in the major receiving regions. When we use particular muscles and senses simultaneously, the main receiving region is more likely to group them together. As a result, it is a key portion of the brain for memory. This explains why you didn’t leap a mile while the cat suddenly poked your elbow; it’s likely happened earlier, so your primary receiving area recognises the collection of stimuli and classifies this as a cat-related event.

Because feeding is essential for life, sensory input as well as motor coordination for the arms and mouth are very closely related. The more sensitive a bodily component is, the more room it gets in the main receiving region. You’ve certainly seen those strange-looking Picasso-like brain drawings that highlight the relationship between various brain regions and bodily components. Sensory and motor homunculi are two types of homunculi. The primary receiving regions of the parietal lobe correspond with sensory input from various sensitive and insensitive body regions.

The neurons in this region of the parietal lobe also interpret data from the opposite part of the body. For example, the right parietal lobe receives information from the left parietal lobe and, conversely,

Parietal Lobe

Somesthetic Association Area

The somesthetic association region is the subsequent parietal lobe functional region. Information from the main receiving region is processed in this section of the parietal lobe. It does, however, have access to another source of data: frontal lobe motor stimuli. The corpus callosum is a ring of nerve fibres that links the two hemispheres of the brain and may also transmit signals between them.

Brodmann area 5 tissue makes up approximately all of the somesthetic association region. This sort of tissue is important for limb movement and our sensation of proprioception. Impaired limb movement and the difficulty of grasping or reaching for objects are common symptoms of damage to this area of the brain.

Parietal Lobe

Polymodal Receiving Area

The polymodal receiving region receives information from the main receiving and somesthetic association areas, as well as motor, visual, and auditory inputs from other lobes’ receiving areas, such as the frontal lobe. Multiple functions are referred to as being polymodal, and this area of the brain has a lot of them. The Brodmann area 7 tissue makes up the majority of the polymodal reception region, which is coupled to a large number of specialised neurons.

BA 7 nerve cells are also polymodal, meaning that each neuron may react to a variety of sensory events. Information from the skin, nose, and ears might all be sent by a single neuron. This is why injury to the polymodal reception region may cause a variety of symptoms, including partial visual loss, discomfort, no pain, slurred speech, aberrant eye movement, decreased proprioception, and/or atypical limb motions.

Parietal Lobe

Granular Insular Area

The granular insular region is the second-to-last link in the parietal lobe chain. Deep-lying insular zones are not generally linked to a distinct Brodmann group.

The parietal, temporal, and frontal lobes all share the insular cortex of the brain. It’s the pale green structure on the left side of the picture below, deep inside the brain. It combines emotion, intellect, motivation, and memory with action and response to arrange numerous inputs and form complex reactions. Stimuli come from all around the central nervous system and enter the insular cortex.

Specifically, smaller quantities of insular cortex tissue are connected to post-traumatic stress disorder (PTSD), particularly in young females. PTSD is an anxiety condition in which the victim re-experiences terrible events from the past. People who practise yoga or meditation on a regular basis have more insular cortex tissue than those who do not. Relaxation practises may help those with PTSD. Because both PTSD and relaxation methods involve various parts of the brain, this is a fairly simplistic example, yet it is comforting to know that we can enhance its function.

Parietal Lobe

Polymodal Assimilation Area

Brodmann area 39 and Brodmann area 40 tissue make up the last functional unit of the left and right parietal lobes.

Damage to Brodmann area 40 in the left hemisphere produces lexical agraphia, or the inability to write words, as well as anomia, or the inability to remember the names of ordinary items. Phonological dyslexia (the inability to sound out words while reading) and phonological agraphia (the inability to sound out the words you are writing) are prevalent if Brodmann area 39 is injured on the same (left) side. Gerstmann’s syndrome is caused by damage to the left hemisphere’s polymodal assimilation region.

Gerstmann’s syndrome has four key symptoms that explain the polymodal assimilation area’s common and distinct activities. These include the inability to write, compute, distinguish right from left, and, curiously enough, detect whether seen fingers are the person’s own or belong to another.

Parietal Lobe Damage

Damage to the parietal lobe may cause sensory and motor symptoms that encompass all of the functions listed in this article, as well as many more. Increased intracranial pressure (ICP) due to infection, burst or blocked cerebral blood vessels (stroke), edoema, or a tumour may all cause damage to the parietal lobe. Depending on where the injury occurs, any of them will cause a section of nerve tissue to die and disrupt brain function.

Damage to Brodmann areas 1, 2, and 3 (the principal receiving region) on the dominant side of the parietal lobe causes a loss of proprioception and fine-touch abilities. Have you ever had a number or a letter traced on your back? You won’t know what they’re writing if the parietal lobe in the main receiving region is destroyed. This is referred to as agraphesthesia.

The owner of the feet in the picture below should at the very least be aware of the difficult drawing’s direction and will most likely identify a few of the forms – possibly a square or circle on the big toe. Without seeing the artwork, it’s likely that the individual will figure out what it’s about (or notice the skeleton foot clue).

Astereognosia is a condition in which you have trouble identifying a familiar item in your hand using just your sense of touch (rather than looking at or smelling it). Astereognosia is also linked to injury to the parietal main receiving region.

Hemineglect, or the inability to recognise objects or even body components on one side of the body, is caused by damage to the non-dominant parietal lobe; the wounded major receiving region will be on the opposite side of the side of neglect.

Damage to the somesthetic association cortex in the left hemisphere implies you won’t be able to move with purpose. The signals that motivate us to move are gone. Damage to the right side of the brain may cause visuospatial problems that impair our capacity to sense movement, depth, and distance.

Many diverse functions overlap in the polymodal reception region. Language and understanding, reading, math, verbal inventiveness, emotion processing, and decision making may all be impacted. The insular tissue’s principal role is to process emotions in conjunction with action and reaction reactions.

If your limbs are injured, you may have trouble distinguishing which posture they are in, leaving you unstable and clumsy. You may not be able to evade a low-flying frisbee if moving objects aren’t correctly analysed. Your sense of creativity will be harmed, and you may develop Gerstmann’s syndrome symptoms.

References

• Tiihonen, J., Rossi R., et al. (2008). “Brain anatomy of persistent violent offenders: More rather than less.” Psychiatry research 163. 201-12. 10.1016
• Jawabri K H, Sharma S. (2020).”Physiology, Cerebral Cortex Functions.” Treasure Island (FL): StatPearls Publishing. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK538496/
• Javed K, Reddy V, Lui F. (Updated 2020). “Neuroanatomy, Cerebral Cortex.” Treasure Island (FL): StatPearls Publishing. Retreived from https://www.ncbi.nlm.nih.gov/books/NBK537247/