Georgia Chiropractic Neurology Center

Brain Based Treatment for the 21st Century!

Written by Sophie Hose, DC, MS, CCSP

Explaining how we see has been a quest that has fascinated researchers for a very long time. With advances in our knowledge of neuroscience, anatomy and physiology and technical progress, studies have shed more and more light on the structures that make up the eye and retina, as well as that pathways within the brain that the visual information travels along in order to be interpreted by us more or less consciously.

Visual processing refers to the ability of the brain to use and interpret visual information from the world around us. Briefly, this is an overview of how this process takes place:

  1. Light gets reflected from objects around us and enters the eye through the pupil. The size of the pupil controls how much light can enter the eye at a time (it gets smaller in bright environments and larger in dimly lit environments). The size of the pupil is controlled by muscles surrounding it, together they make up the colorful iris of the eye.
  2. Inside the eye, the light hits the retina at the back of the eye. The retina contains two types of receptors: Rods and cones. Rods are more responsible for detecting dim lights and are therefore used for night vision. Cones are more responsible for vision in brighter environments and enable us to see colors.
  3. All light receptors (rods and cones) synapse (aka communicate with) on the optic nerve through other cells that span the distance between them. The optic nerve then exists the back of the eye in a spot called the blind spot (this spot on the retina does not contain any light (photo) receptors because it contains only optic nerve fibers).
  4. From there, the two optic nerves (one from the left and one from the right) meet and partially cross over to the opposite side in a structure called the optic chiasm. The reason why some fibers cross, is so that both eyes and both sides of the brain can be affected by visual information only visible from one eye. For example, when an examiner shines light in only one eye, both pupils should constrict. Also, generally one side of the brain is more responsible for controlling and monitoring the opposite side of the body (eg. Right brain controls left body). The same goes for visual information. What is visible in the right visual field, will mainly be processed by the left brain.
  5. From the optic chiasm, the information travels deeper into the brain along what is called the optic tract. Some branches synapse in the midbrain (specifically the superior colliculi) to – amongst other things – coordinate eye and head movements based on the visual input and control the size of our pupils. The majority of the fibers travels to the thalamus. The thalamus is considered the sensory relay station of our brains. All sensations that we experience anywhere in our body eventually pass through the thalamus before they are processed in higher cortical structures, such as the parietal lobes, as discussed in our last blog post.
  6. After passing through the thalamus, the visual information travels along the optic radiations to the occipital lobes at the back of our brains. The occipital lobe is considered our primary visual cortex, meaning that this is where the initial visual processing takes place. It is highly specialized for processing information about static and moving objects and is excellent in pattern recognition. It also processes color, shape, motion and location of what we are seeing.
  7. The information about color, shape, motion and location is then sent to two different areas in the brain for further processing:
    1. The dorsal stream connects the occipital lobes to the lower parietal lobes and the upper temporal lobes. In these areas, information about the location and movement of what we are seeing is further integrated with our own perception of where we are in the world and where the object that we are seeing is located in reference to us. This pathway is also called the ‚where‘ pathway.
    2. The ventral stream connects the occipital lobes to the lower temporal lobes. There, the information about the shape and color of the object we are looking at is processed. This is where we recognize objects and familiar faces, as this area is just adjacent to our memory centers. This pathway is also called the ‚what‘ pathway.

Because of this lengthy pathway among which visual information travels from our eyes to the back of the brain and slightly forward again, there are many different locations where a ‚lesion’, a region that has suffered structural or functional damage, can affect our ability to process the information that we see. This means that although there might not be any problem with our eyes, we might still not be able to ‚see‘.

In concussions, some of the possible symptoms associated with problems of the visual pathways and especially the occipital lobes include the following:

  • poor depth perception
  • headaches
  • fatigue
  • blurred near vision
  • spatial disorientation
  • light sensitivity

When classifying these kinds of concussions according to the five subtypes, concussions affecting vision could fall under the oculomotor, the cognitive and the headache categories.

There are a lot more symptoms that are related to vision, such as double vision, poor eye tracking, difficulty shifting gaze from one point to another and others. These symptoms are primarily related to areas in the brain that control the movement and alignment of our eyes, namely the brainstem. We will spend more time discussing this area of the brain in a future blog post.

Fatigue is one of the most commonly experienced symptoms following a concussion. An effective official treatment for this fatigue is lacking and so is the understanding of its underlying mechanisms. In a study done at the University of Groningen in the Netherlands, researchers assessed whether the amount of neural activity necessary to maintain a motor task (a certain movement) is the same in healthy participants versus participants that suffered from a concussion and are now experiencing persistent fatigue. The researchers found that there were no signs of compensatory cortical activation in order to maintain performance. The difference that they did find however was that concussed participants reported significantly greater levels of fatigue with the same task. Furthermore, functional MRI data revealed that areas of the brain that are associated with attentional visual processing show increased activation when the concussed participants reported greater levels of fatigue. This could be interpreted as ‚normal‘ levels of visual processing related to daily tasks requiring more energy to be maintained, leading to fatigue with seemingly small activities.

A similar selectively increased activation in brain areas related to visual processing and vestibular processing (these areas integrate information from the inner ear related to our position and movement in relationship to gravity – highly involved in vertigo) was noted in a different study assessing the processing of complex visual stimuli (different videos) in patients with postconcussive visual motion sensitivity. The researchers concluded that visual input had an increased weighting into the vestibular network which caused the participants to have increased symptoms of vertigo.

What connects these two studies is that in both cases, seemingly unrelated symptoms (vertigo and fatigue) are highly impacted by problems in the visual processing abilities of the concussed participants. These outcomes once again highlight the incredibly complex interconnectivity of our brains and how no area of the brain works by itself. All of our senses are integrated together to form a picture of the world around us and any mismatch of these senses will lead to symptoms, whether that be vertigo or something else. At the same time, if one area needs to compensate for a lesion either directly in that area or somewhere ‚pre-synaptic‘ to it (located earlier in the pathway leading up to the compensating area), this compensation will have potentially detrimental effects on seemingly unrelated functions of the brain. Understanding these connections and establishing an effective treatment plan can be very challenging and takes a battery of comprehensive testing to accurately assess the function of a multitude of brain regions.

At GCNC, we have made it our goal to examine our patients in the most detailed and specific way possible to determine exactly where the dysfunction occurs and what effects it has on the patient’s well being. This examination starts at the history taking, as detailed questions can sometimes already shed a light on the problematic area, especially for our highly educated and experienced doctors. We then follow up with an assessment of the autonomic nervous system, the oculomotor system, the vestibular system, cognition and a comprehensive neurological exam. This allows us to create a specialized treatment plan for each patient to allow them to return to their life as quickly as possible.

If you or someone you love has suffered a concussion and you would like to learn how chiropractic neurology can help, contact the team at Georgia Chiropractic Neurology Center today. We look forward to hearing from you!

Sources:

-Allen JW, Trofimova A, Ahluwalia V, Smith JL, Abidi SA, Peters MAK, Rajananda S, Hurtado JE, Gore RK. Altered Processing of Complex Visual Stimuli in Patients with Postconcussive Visual Motion Sensitivity. AJNR Am J Neuroradiol. 2021 May;42(5):930-937. doi: 10.3174/ajnr.A7007. Epub 2021 Feb 11. PMID: 33574098; PMCID: PMC8115356.

-Prak RF, Marsman JC, Renken R, van der Naalt J, Zijdewind I. Fatigue following mild traumatic brain injury relates to visual processing and effort perception in the context of motor performance. Neuroimage Clin. 2021;32:102783. doi: 10.1016/j.nicl.2021.102783. Epub 2021 Aug 13. PMID: 34425550; PMCID: PMC8379650.