Written by Sophie Hose, DC, MS, CCSP
The temporal lobes are located below the parietal lobes on the sides of the brain, directly behind the ears. When it comes to their function, the temporal lobes are mainly regarded as the location of auditory processing (hearing) and memory integration. However, the temporal lobes are also highly involved with the processing of emotions and through the connection with the brainstem, these emotions are experienced in the form of bodily changes (eg. Changes in heart rate, sweating, blushing, hairs standing up, a funny feeling in the stomach (due to changes in peristalsis, movements of the bowels)).
Hearing is processed mainly in the primary and secondary auditory areas, which are located in the lateral portion of the temporal lobes. More medial (aka more midline), a group of structures are located that together make up the limbic lobe or limbic system. These structures include the amygdala, the hippocampus, the uncus, the dentate gyrus and the parahippocampal gyrus. The limbic system is fundamental in the processes of learning, memory and in the regulation of emotions.
More specifically, the amygdala is involved in emotional processing, especially fear and aggression. It has been hypothesized to be involved in a variety of other conditions (such as autism spectrum disorder). The hippocampus (from Greek: sea horse – due to its shape) is highly involved in the creation and storing of memories. In cases of damage to the hippocampi, the patient often experiences forms of amnesia – either anterograde (cannot form new memories) or retrograde (cannot remember old memories). The parahippocampal gyrus also is involved in memory encoding and retrieval.
Keeping these broad functions of the temporal lobes in mind, it becomes obvious that in the case of damage to one or both of the temporal lobes in a concussion, a multitude of symptoms can evolve. These symptoms include but are not limited to:
- memory loss
- trouble forming new memories
- forgetfulness
- sound sensitivity
- increased emotionality
- excessive fear or aggression
- changes in personality
- trouble with auditory processing
To classify these kinds of concussions according to the five subtypes, temporal lobe concussions most commonly fall under the cognitive or anxiety/mood categories.
We had previously briefly discussed the Baltimore Longitudinal Study of Aging in this blog post. The study specifically researched the lasting effects of concussion on the aging brain, with a focus on the frontal and temporal lobes as most neuroimaging studies show effects of concussions in these areas of the brain. The reason for this study is that previous research has repeatedly suggested a correlation between concussions and increased risk of neurodegenerative disorders, such as chronic traumatic encephalopathy and Alzheimer’s disease. In the Baltimore Longitudinal Study, the researchers used MR imaging, DT imaging, PET studies and a battery of neuropsychological tests to assess the brain function of the participants, comparing individuals with a history of concussion to those without. This study is especially interesting because the average time that had passed since the individual had sustained the concussion was 23 years and each participant underwent multiple repeated assessments over a time span of about six years. This means that the researchers were able to truly study the lasting effects of concussion and how they developed over the years.
Before discussing the outcomes of this study in regards to changes in the temporal lobe, let’s briefly talk about DTI.
Diffusion Tensor Imaging (DTI) is a form of MRI (magnetic resonance imaging) that measures water molecule diffusion and its directionality. That means, it measures and depicts the exchange of water molecules between cells and thereby creates a map of the body’s internal structures. The two organs that it is most commonly used for are the kidneys and the brain. In the brain, the result is a beautiful rendition of what is called the white matter, the tracts that connect our neurons to each other. A tract is made up of several neuronal axons and dendrites, the small ‚arms‘ that neurons use to form synapses (neuronal connections) with each other and connect and communicate. If you have been at our office before, you might have seen some of the artwork that we have on display. There are multiple images that are DT images of real brains, below you can find an example:
In the Baltimore Longitudinal Study of Aging, the main findings of the researchers were that participants with a prior concussion had greater brain atrophy (wasting away of cells, in this case neurons) in temporal lobe white matter and the hippocampus during the first imaging 23 years after the initial concussion, as well as the microstructure of the white matter in multiple brain regions. In addition to that, changes in blood flow to different regions in the brain were noted (both increases and decreases) but no significant changes were observed in the neuropsychological tests that were administered. The differences between the two groups of participants were mostly observed during the first examination by the researchers and they remained relatively stable throughout the follow up exams over the span of the study.
Brain atrophy is associated with a multitude of conditions, such as injury, infection, dementias, stroke, cerebral palsy or Huntington’s disease. In mild cases, the patient may experience relatively little effects of the atrophy in daily functioning. In more severe cases however, symptoms such as seizures, aphasia and dementia may occur.
In this study however, the cognitive performance of the study participants was not significantly impacted by the changes in temporal lobe volume and the changes in the white matter microstructure. Although the researchers concluded that concussions lead to long-term structural and functional alterations in the brain, the participants were still able to function in everyday life. Another positive finding was that although these atrophic changes in brain volume have been observed repeatedly across multiple studies, the changes seem to be stable and not progressive (as for example seen in Alzheimer’s disease). The same is true for changes in the microstructure of the white matter of the brain. To this day, the exact significance of these changes in white matter microstructure remain unclear, however they are hypothesized to be an effect of the adaptive changes that the brain undergoes after injury (more about that later).
Directly following a concussive injury, changes in brain metabolism and therefore in blood flow to and within the brain have been observed. Generally, the metabolic demand of the injured tissue goes up (meaning that more nutrients and therefore more blood flow are required) for a certain amount of time. In more chronically symptomatic cases, both increases and decreases in cerebral blood flow have been observed. This study however found the same was true for participants that were no longer experiencing the magnitude of symptoms they had suffered from originally following the concussion. Given that the researchers did not find significant changes in the neuropsychological tests they ran, the observed changes in blood flow to the brain might actually be another form of compensation for the injury that was sustained, rather than be the reason for sustained symptomatology. Previous studies have observed persistent functional deficits in participants with decreased blood flow to the frontal and temporal lobes so the here observed increase might be the reason why the participants of the Baltimore study were able to compensate for their functional deficits.
In regards to Alzheimer’s disease, extensive brain atrophy is considered one of the final stages of this progressive disease. In smaller amounts, atrophy can be seen in early and even pre-clinical stages, resulting from significant cell death following the deposition of what is called amyloid plaques and neurofibrillary tangles within the brain tissues, as well as neuroinflammation impeding the normal function of the brain.
Chronic Traumatic Encephalopathy (CTE) is characterized by the progression of tau in the frontal and temporal lobes and extensive atrophy in the later stages of the disease.
This study has shown that following a concussion, there may be what the researchers called selective vulnerability of the frontal and temporal lobes, however further research is needed to follow up on the rate of dementia onset of patients with a history of concussion, given that the sample of participants in this study did not show any cognitive deficits. Even though the study may not leave us with final answers in regards to the correlation between concussion and neurodegenerative disease, it definitely showed that a concussion is not a transient (lasting only a short time) injury. In fact, it has long-lasting effects on the maturing and aging brain that might not always be noticeable to the patient or their loved ones. Every concussion, as minor as it may seem should therefore be properly assessed and treated by a skilled clinician to avoid potentially detrimental effects in the time immediately following the injury, as well as many years later.
The research on the treatment of concussion and its long-term benefits is still ongoing with new studies being published every year. Our doctors at Georgia Chiropractic Neurology Center continuously attend seminars and conferences to learn and share their knowledge of a variety of conditions, including concussions, to best tend to our patients. 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:
–June D, Williams OA, Huang CW, An Y, Landman BA, Davatzikos C, Bilgel M, Resnick SM, Beason-Held LL. Lasting consequences of concussion on the aging brain: Findings from the Baltimore Longitudinal Study of Aging. Neuroimage. 2020 Nov 1;221:117182. doi: 10.1016/ j.neuroimage.2020.117182. Epub 2020 Jul 20. PMID: 32702483; PMCID: PMC7848820.
-Patel A, Biso GMNR, Fowler JB. Neuroanatomy, Temporal Lobe. 2023 Jul 24. In: StatPearls
[Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan–. PMID: 30137797.