COGNITION PART 1: TERMINOLOGY AND IMPACT AFTER CONCUSSION

WHAT IS COGNITION?

Cognition is the process of thought, knowledge, learning, and problem solving. This includes the capacity for thought, which goes beyond the simple perception of the world. Cognition also includes the multiple domains of function that go into the ability to acquire and possess knowledge and then to use it to manipulate the world through our actions and behaviour.
 
It is important to note that there has always been disagreement about the categorization of function, but let us break this down into the following domains.

COGNITIVE DOMAINS

Orientation. We can also call this basic awareness. Orientation is your knowledge of
 a) who you are;
b) where you are, your environment; and
c) when you are, a sense of time.
Attention. This is a function that requires both a state of arousal or alertness and in essence is your ability to attend to stimuli in your environment. There are several levels of attention to be considered.
  1. Focused attention. This is your ability to perceive, and acknowledge, specific information from your environment. For example, this is noticing that your housemate has added a new fridge magnet to your collection.
  2. Sustained attention. This is your ability to maintain attention over a period of time during a continuous activity. For example, this is your ability to read this article right now, you have probably already been reading for about a minute, good for you!
  3. Selective attention. This is your ability to process information selectively. To do this you need to both be able to inhibit attending to the irrelevant stimuli, while attending to the target stimuli. For example, this is your ability to focus on the conversation that you are having with your friend at the bubble tea place, when the couple at the table beside you is having a very interesting fight, but you focus on your friend (again, good for you!).
  4. Alternating attention. This is your ability to shift focus between tasks that demand different behavioural or cognitive skills. For example, you are at the gym (good for you) and are working out on a machine, when you are done that set, you talk to your friend, then you do your next set, you switch between those two things.
  5. Divided attention. This refers to your ability to respond to two or more events or stimuli simultaneously. For example, you are driving to work and are able to focus on the road, oncoming traffic, signs, other moving objects in the vicinity, hear the horns, and think about how to get where you are going, all at the same time.
Memory. This is your ability to encode, store, and retrieve information. It is the reason that you can learn. Again within this domain, there are many different types of memory, here are a few that are relevant to our purpose.
  1. Short-term memory. This is the capacity for storing information or stimuli, for, you guessed it, a short period of time. For example, short-term memory is used when you are chatting with a cute girl and remember their phone number, because they just told you.
  2. Working memory. This is more of an active process, and typically refers to the manipulation of information or stimuli, above and beyond the storage of it. For example, that cute girl told you her number, and now you have to work to keep it in your memory before you get out your phone and type it in.
  3. Long-term memory. This is the division of memory responsible for information that is held for a long-term, or indefinitely. This includes explicit memory (aka declarative), which is the information that you can consciously recall, like past experiences (episodic memory) and facts (semantic memory), and also implicit (aka procedural) memory, which is your ability to remember unconsciously, for example how to ride a bike. We can also think about prospective memory, which is your memory for things that have yet to happen (e.g. I have an appointment with my OT on Wednesday), and retrospective memory, which is memory for things that have already happened (e.g. I had an appointment with my OT yesterday).

Executive Functioning. This is more of a complex domain and essentially is a grouping of all higher level cognition. This is higher level cognition, because in order to complete executive functions, you will need to use the basic functions of attention and memory. Executive function can include reasoning (deduction and induction), sequencing and planning, forming concepts, abstract thinking, and problem solving. For example, when you are playing Settlers of Catan (or any boardgame) with your friends and you block your friends from building anything, while scoring points yourself.

 
Processing Speed. This is the time it takes you to perform a cognitive function or task. For example, your friend asks you how many years you have been playing the flute, processing speed is how long it takes you retrieve that information from memory, or do the mental math necessary. On any task there is a trade off between accuracy and processing speed. Think about being a goalie in soccer when someone is kicking a ball toward your net. You can either act faster, committing to the location you think the ball will be, and risk the greater chance of being incorrect, or you can act slower, and likely be more correct, but also be more likely to miss the ball.
Metacognition. This is your ability to think about your thinking. Metacognition is how we know that we make errors, or how we choose certain cognitive strategies to use in different situations. For example when you have to learn a phone number, a common strategy to use is repetition, you repeat the number until it sticks in your memory. Knowing to use that strategy requires you to have metacognition, awareness about your own cognition.
Social Cognition. Now there is some debate as to whether social cognition is a separate entity or whether it is simply “cold” cognition with added context. Regardless, social cognition is an important part of your health because these are the functions that allow you to interact with the other people in the world. Social cognition includes the following abilities.
  1. alexithymia, which is your ability to recognize and describe emotions in yourself;
  2. recognize cues, which includes verbal (e.g. voice tone) and nonverbal (e.g. facial expressions);
  3. be empathetic, which can be either cognitively by understanding the context and emotions (e.g. you know that your friend is disappointed when her favourite ice cream flavour has sold out), or emotionally by experiencing those emotions yourself (e.g. your friend just experienced a loss and they feel sad, you then also feel sad); and
  4. make inferences, or use theory of mind, to know what others may be thinking and feeling (e.g. my friend is happy because he just won an award for being a superstar athlete).
It is important to note that when we say “cognition” this is different from the other brain functions. Neurology is important, as is psychology, and these factors do interact with cognition, yet when we say “cognition” we refer purely to these domains and to your ability to think.

HOW IS COGNITION IMPACTED AFTER CONCUSSION?

The relationship between concussion and cognition is a complex one. With the research on chronic traumatic encephalopathy and the testimonials of famous professional athletes, the impact of concussion on cognition has become an increasingly large concern to individuals and topic in research. There are many studies on cognition and concussion, but many are conducted on samples that, are small, centred on professional athletes or individuals with multiple concussions, military, and include mostly male participants.

A recent systematic review of meta-analyses (Karr, Areshenkoff, & Garcia-Barrera, 2014) found that the effect sizes, which indicate the magnitude of statistical relationships between concussion and the specific cognitive domains impacted, were incredibly variable between reviews on research. This can lead us to draw the conclusion that the impact on cognition is quite global, although there may be a greater degree of impairment to the specific domain of working memory. Their review also found that there was not much evidence of difference between one or multiple concussions, although executive functioning was the domain most affected by multiple impacts. As we could predict, the cognitive impairments are generally more severe during the acute phase (especially within a week after injury), with sports related injuries possibly resulting in faster cognitive recovery.

One very difficult limitation to get around is that of the inability to know baseline function. When an individual has a concussion, it is very possible to have them complete a neurocognitive battery, which can compare their performance to population norms, but it is next to impossible to know how they would have performed on the tests prior to the injury. This means that self-reported differences in functioning do need to be taken into consideration, and when they are, it is possible that cognitive impairment after concussion is underestimated by the larger reviews on the research, as a trial of measures post-concussion found that over half of patients do report a difference in cognition from baseline, six months post injury (Ngwenya et al., 2018).

While people are reporting this impact to their cognition, the good news is that it is likely, based on the review of the meta-analyses (Karr et al., 2014), cognition returns to the baseline levels within 90 days of the injury, or even more rapidly – within 1-2 weeks – in a majority of individuals (McAllister & McCrea, 2017). It is possible that there a small subgroup of individuals (possibly approximately 10%) for whom cognition continues to remain slightly impaired long-term, and these individuals, while not well studied in regards to cognition, are more likely to be those with previous impacts, psychological disorders, female, and those injured in a motor vehicle accident.

Another large concern, is the fact of multiple concussions. It makes sense that if you continually are exposed to hits to the head as a NHL hockey player, or blasts as a soldier, you would be more likely to have cognitive impairment. The review of the meta-analyses mentioned above (Karr et al., 2014) did find that multiple concussions may predict a longer recovery period. There is some conflicting evidence, even at the level of recent reviews of research, about the state of cognition after multiple concussions with some research indicating greater levels of impairment, and other research indicating no difference (McAllister & McCrea, 2017; Yumul & McKinlay, 2016). Another recent reviews indicated that there may be an impact on visual memory (worse with multiple impacts), but otherwise there is no difference on cognitive testing between individuals with a history of concussion, compared to a first concussion (Alsalaheen et al., 2017).
The conflicting results between individual studies, and even between recent reviews of research, makes it very difficult to draw conclusions about the state of cognition after concussion, but in summary here is what is likely.
  1. Most individuals will experience some cognitive impairment during the acute phase after a concussion. 
  2. This cognitive impairment in the acute phase is more global, not specific to one domain of functioning, but perhaps working memory is slightly more impacted than other domains. 
  3. Almost all individuals will return to baseline cognitive functioning after a concussion, and this is, for most, within 3 months of the impact. 
  4. There might be an effect of multiple impacts leading to a greater degree of cognitive impairment and/or a longer recovery back to baseline.
Therefore we need more research and ideally prospective studies, ones that would measure baseline functioning, and then evaluate the recovery process after concussion, should it occur.
Alsalaheen, B., Stockdale, K., Pechumer, D., Giessing, A., He, X., & Broglio, S. P. (2017). Cumulative effects of concussion history on baseline computerized neurocognitive test scores: Systematic review and meta-analysis. Sports Health, 9(4), 324-332. doi: 10.1177/1941738117713974   Karr, J. E., Areshenkoff, C. N., & Garcia-Barrera, M. A. (2014). The neuropsychological outcomes of concussion: A systematic review of meta-analyses on the cognitive sequelae of mild traumatic brain injury. Neuropsychology, 28(3), 321. doi: 10.1037/neu0000037   McAllister, T., & McCrea, M. (2017). Long-term cognitive and neuropsychiatric consequences of repetitive concussion and head-impact exposure. Journal of Athletic Training, 52(3), 309-317. doi: 10.4085/1062-6050-52.1.14   Ngwenya, L. B., Gardner, R. C., Yue, J. K., Burke, J. F., Ferguson, A. R., Huang, M. C., … & Mukherjee, P. (2018). Concordance of common data elements for assessment of subjective cognitive complaints after mild-traumatic brain injury: A TRACK-TBI Pilot Study. Brain Injury, 32(9), 1071-1078. https://doi.org/10.1080/02699052.2018.1481527   Yumul, J. N., & McKinlay, A. (2016). Do multiple concussions lead to cumulative cognitive deficits? A literature review. Physical Medicine & Rehabilitation, 8(11), 1097-1103. http://dx.doi.org/10.1016/j.pmrj.2016.05.005
Last update: March 2019