Causality is the foundation for critical thinking in physiology

Not long ago, I posted a newsletter focused on “Thinking as a learning objective”. There, I related the importance of critical thinking to clinical care as evidenced by changes to the medical college admissions test (MCAT) and the National Council Licensure Examination (NCLEX) for nursing. I also emphasized a necessary focus on qualitative reasoning skills and the need to explain physiological concepts from the basis of their inherent logic such that application of knowledge becomes achievable by our students. What’s frequently missing from physiology course curricula are the specific mechanisms of doing so, including an understanding of the relationships between cause and effect, reasoning, and predictive power.

David Hume, the Scottish enlightenment philosopher, wrote about inductive reasoning wherein predictions about unobserved things are based upon observation of prior events. In essence, inductive inferences link the unobserved to the observed. Hume noted that there is no way to fully justify these inferences, yet we all make them. Hume also posits that all predictions involve causality and that the relation between cause and effect solely provide this predictive power, allowing us to go beyond memory and the senses. The qualitative reasoning ability I mention above, and find so very important, is highly dependent upon an understanding of causality between the events of what I like to call “physiological cascades”. These cascades are the strings of events triggered by perturbations of physiological systems and can include elements and actions of physical, chemical or biological players (example below). It’s important to recognize that “causes” can be sufficient, necessary, or contributory.

So, what does it mean to explain something from the basis of its inherent logic? Some of this is discussed in our recent AJP paper, but I will provide an expository example here. We all teach physiological and associated anatomical content and concepts. This is the observed and described factual knowledge of our field. For example, ADH is a hormone released by the posterior pituitary in response to dehydration-induced hyperosmolarity (which would lead to hypovolemia-mediated hypotension in the absence of sympathetic support). ADH then activates the insertion of aquaporins at the collecting duct membranes in the kidney, increased renal H2O reabsorption, and a return of ECF volume toward normal. We can then construct a concept map (flow chart) wherein the downstream actions are logically sequenced.

Students are often overwhelmed by the sheer volume and novelty of the content we teach. If we want them to gain useful skills in the utilization of this content (which should be our primary goal IMO) then how we structure this content within our explanations is absolutely crucial. As I am apt to tell my students, it would be difficult to recall all 100 words in a random list, however, what if they were in the form of a paragraph? Not only would you recall more of the words, but you’d learn something additional, and more important than any individual word, conveyed by their relationship to one another in the text.

The problem is that we often leave out meaningful explanations of the causal linkages between elements seen in the map. Instructors often give some explanations for why one thing leads to the next, but they just aren’t consistent or complete enough for students to get the whole picture. Sometimes we (and even our teaching references) totally skip key content steps, making conceptual leaps the students are incapable of following (what if we left out increased blood and venous volume in our first ADH concept map?). Omissions such as these tend to promote attempts at rote memorization by students rather than guiding them to real understanding of the material. Citing a concept map’s key elements and providing thorough explanations of their causal relationships are both essential to real comprehension (expanded map coming up).

While the context of ADH secretion (response to dehydration) was provided above, the cascade of downstream effects and their causality are critical elements requiring finesse in classroom discussions. We must take the factual elements of anatomy and physiology (ADH, AQP-2, gradient driven flux, molecular mechanisms of cardiac contractility, hemodynamics, etc.) and tie them together within conceptual frameworks that really make sense to learners. These frameworks are not simply lists of facts but rather a logical story with rational elements playing essential roles to achieve a goal. Additionally, each step creates a physical, chemical or biological instigation for the next. As Hume stated, it is causality, the linkage between cause and effect, that provides predictive power and the ability to move beyond memorization. Similarly, perturbations at any step along the way can then be rationally assessed and logical outcomes anticipated once the rationale of each transition is understood. What took me years to fully appreciate was that many students struggle not with the elements of a cascade but with the rationale for its sequence (the links!). In fact, students often provide illogical explanations for these links which are actually counterproductive to their ability to apply knowledge and predict outcomes. For these students, higher order critical thinking questions are quite baffling (while they may do just fine on questions focused on the factual content or even the order of events within a cascade). Construction of concept maps containing their inherent rationale is essential for laying the foundations of critical thinking. Given that, a more complete diagram of the ADH pathways, resulting in a really meaningful map, integrating the elements and their causality, would look more like this …

Note that, even here, there are elements that could be expanded or added to develop an even more complete picture! One could eventually link this map with one generated for angiotensin II and another for aldosterone (or other related players) showing areas of integration as well as functions distinct to each hormone, much like a giant physiological Venn diagram. The bottom line is that the level of detail and interrelationships among the pathways included in the map are up to the instructor’s discretion, but the comprehensive outcome must be completely logical and convincing.

So, what do students need to do for all this to work? First, I would say that because there are obvious differences in the level and complexity of physiological content there needs to be a variety of mechanisms employed to master this subject. Given that complex functions are comprised of linked factual elements, the learning of factual content is fundamental. I even advocate use of flashcards or other memory tools when working at this level. Having said that, what goes on a flashcard may change over time as the student realizes what essential elements are required once those facts become players in a broader scheme. Next would be to generate the concept maps or flow diagrams that link the factual items, often sequentially, when acting in the performance of a homeostatic or mechanistic “task”. Then comes the part most dependent upon us, the addition of causal links that provide the rationale for the sequencing – THIS is actually explaining physiology. Finally, students need to practice, first with normal perturbations to the system (e.g., drink a liter of water) and then, especially in higher level application-focused courses, with dysfunction (e.g., nephrogenic diabetes insipidus) of the system itself and how it would respond, or not, to perturbations. The latter would involve the generation of novel concept maps with, in many cases, pathophysiological outcomes.

Lastly, both formative and summative assessment should align with the content and skill-based goals of teaching in this fashion. Certainly, one cannot ask predictive questions if causal logic is absent. When such lucidity is present, however, students still need to be trained to think in ways that require them to employ that logic. For this reason, I recommend formative assessments that are, if anything, even more focused on application than recall. There is evidence to suggest that challenging students by using higher order assessment tools aids in the development of those very skills. In fact, doing so not only increases student performance on application, evaluation and analysis style questions but also enhances memory of factual information. Even factual content should be tested in context as this avoids reliance on pure memorization alone. What I mean by this is presentation of factual content in novel situations, requiring an understanding of meaning that allows generalization of the concept, not simply matching of terms to definitions previously presented.

In closing, teaching students to think about physiology enables them to think rationally about the functioning of any dynamic system, be it their car or their liver! In this way we train them not only for careers in life sciences but for life itself.

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