Written by Sophie Hose, DC, MS, CCSP
This post explores the role of the parietal lobe in mild traumatic brain injuries, commonly known as concussions. While the frontal lobe is often the most affected in concussions, symptoms can manifest across all regions of the brain for several reasons:
- Direct Impact: Any part of the brain can be directly affected by impact, either from an external object hitting the head or from the brain colliding with the inside of the skull due to a rapid change in acceleration. This is known as a coup, from the French word for “hit.”
- Counter Coup: Often, a coup is followed by a counter coup, where the brain rebounds from the initial impact site, colliding with the opposite side of the skull. Although this secondary impact is less forceful, it can still cause physiological or, in severe cases, physical deficits.
- Brain Networking: Recent research has shown that no single area of the brain functions in isolation. Instead, all regions must work together to ensure smooth and accurate functioning. This interconnectedness has led to the concept of brain networks, where specific functions like movement, sensation, or visual processing involve multiple brain regions. This means that even an injury to a distinct brain area can lead to deficits in seemingly unrelated physiological processes.
The Parietal Lobe
The parietal lobes, located at the top of the head, are crucial for processing sensory input. They integrate sensations from the body that inform us about our position in space, the relationships between different body parts, and the surrounding environment. These sensations can be categorized into four main types:
- Discriminative Touch: This involves recognizing objects by touch, including their shape, weight, smoothness, pressure, location, and movement. In clinical settings, we test this by drawing letters or numbers on your hands and legs or by touching you with one or two fingers.
- Proprioception: Proprioception refers to the brain’s ability to sense the location of body parts in space. Even with your eyes closed, you should know where your hands are in relation to your chest, thanks to proprioception. This ability is tested by assessing joint position sense, where we bend a finger or toe and ask you to identify the direction of movement.
- Nociception: Nociception is the perception of pain. Since pain is a subjective experience influenced by various factors, no specific “pain receptors” exist. Instead, sensory inputs are interpreted as painful based on our unique physiology. We test nociception by asking you to distinguish between sharp and dull objects touching your skin.
- Temperature Sense: The ability to differentiate between temperatures is crucial for survival. We test this by touching your arms, legs, and face with hot and cold packs to see if you can distinguish between the two.
Parietal Lobe Functions and Concussion Symptoms
The parietal lobes are part of the brain’s overall networking system, integrating sensory information from surrounding lobes, including vision (from the occipital lobes) and hearing (from the temporal lobes). A key area within the parietal lobes is the primary somatosensory processing area, where neurons are associated with different body areas. These neurons are arranged in a somatosensory homunculus, a brain map representing the body. Some areas, like the fingers, have more representation due to the density of neurons.
Common Symptoms Following a Parietal Lobe-Related Concussion:
- Changes in sensation (e.g., difficulty distinguishing dull and sharp, numbness, or tingling)
- Pain syndromes not linked to physical injuries
- Headaches
- Clumsiness or bumping into objects
- Difficulty orienting in space
- Neglect syndromes (rare; failure to integrate sensory input appropriately)
- Balance problems
- Difficulty coordinating the body
Most concussions affecting the parietal lobes fall under the vestibular or oculomotor category, but clear-cut classification is challenging.
Research on Postural Control and Balance in Concussion
In 2021, the Journal of Sports Medicine published a study on persistent deficits in postural control and balance among student athletes who recently suffered a concussion compared to those with a history of concussions. The study assessed the students’ ability to stand still without swaying under different sensory conditions, such as with eyes open or closed or on a vibrating platform versus firm ground.
Our ability to balance relies on sensory input from our:
- eyes (vision),
- inner ears (vestibular system), and
- body (proprioception)
Normally, if one sense is compromised (e.g., closing your eyes), the other two compensate to maintain balance—a process known as sensory reweighting. However, the study found that participants with a history of concussion relied more on visual and vestibular inputs than proprioception. Although the physiological mechanisms underlying these postural control impairments remain poorly understood, balance and postural control are often significantly affected after a concussion.
Many standard clinical tests, such as the BESS test, assess a patient’s ability to balance under different sensory conditions. However, these tests do not indicate which of the three sensory systems related to balance is deficient. At GCNC, we use our Virtual Reality system to perform a Modified Clinical Test of Sensory Interaction in Balance (mCTSIB). This allows us to identify which of the three senses involved in balance are intact or impaired, enabling the development of appropriate rehabilitation and reassessment procedures. This technology is particularly beneficial as it can detect impairments that might go unnoticed in traditional clinical testing, which relies solely on the visual observation skills of the tester.
Importance of Detailed Assessments in Concussion Recovery
When determining whether a patient can safely return to activity after a concussion, detailed assessments are crucial. Research has shown that patients are 2-3 times more likely to suffer another concussion or musculoskeletal injury after an initial mild traumatic brain injury (mTBI). This increased risk is attributed to maladaptive sensorimotor control, where a not fully recovered patient might experience deficits in processing sensory information and/or generating appropriate motor responses.
Sources:
- Functional Neurology For Practitioners of Manual Medicine – Randy Beck
- Caccese JB, Santos FV, Yamaguchi FK, Buckley TA, Jeka JJ. Persistent Visual and Vestibular Impairments for Postural Control Following Concussion: A Cross-Sectional Study in University Students. Sports Med. 2021 Oct;51(10):2209-2220. doi: 10.1007/s40279-021-01472-3. Epub 2021 Apr 21. PMID: 33881749; PMCID: PMC8449812.