Microglia and Neurons by GerryShaw CC BY 3.0 https://commons.wikimedia.org/wiki/File:Microglia_and_neurons.jpg

Where Does “Bottom-up” Bottom Out?

(Image credit: “Microglia and Neurons” by GerryShaw licensed under CC BY 3.0)

‘Bottom-up’ and ‘top-down’ are staple concepts in cognitive science. These terms refer to more than one set of concepts, depending on the context. In this post, I want to talk about one version of ‘bottom-up’ and try to pin down what is at the “bottom” of cognition.

First, I should single out the meaning of ‘bottom-up’ that I have in mind. It is the one in which ‘bottom’ refers to the deterministic hardware and pre-conscious processes from which “higher level” processes like meaning, affect, and perhaps conscious awareness emerge. On a common view, the “bottom” might be the brain or some part(s) of the brain. On this view, the organic tissue and the electro-chemical stuff that happens within are the “bottom” from which meaning, affect, and conscious awareness might emerge.

Just how meaning, affect, and conscious awareness is supposed to emerge from this “bottom” is not what I wish to talk about here. Rather, I want to think about what we should take to be at the “bottom” of meaning, affect, and conscious awareness—henceforth, I will use ‘bottom’ without quotations.

I have already mentioned a common view: the brain is the bottom. On this view, one assumes that in order to understand the mechanisms underlying meaning, affect, and conscious awareness, we will need to look at the brain. However, the brain is studied at various levels of detail.  For example, people study regions of the brain, individual neurons, electrical- and light-induced events within isolated neurons, the underlying biology of neurons, and the underlying chemistry of the biology of neurons.  All of these analyses presuppose that the brain is ultimately the bottom since the phenomena in question seem to exist only brains (e.g., brain regions and neurons).

But perhaps there are reasons to think that there are features of the brain that are not exclusive to brains and that these features are the bottom of bottom up processes. In other words, perhaps we haven’t quite reached the bottom. Before we consider this possibility, we will need to make a distinction. There are at least two ways to dispute the claim that a particular thing is not actually the bottom:

    1. The bottom isn’t just [the proposed bottom]. It’s that plus some other stuff, the sum of which comprises the same bottom level (e.g., the brain and the rest of the body).
    2. The bottom isn’t [the proposed bottom]. The bottom is actually below that (e.g., not molecules, but atoms; not atoms, but atomic particles, etc.).

Both kinds of dispute are important and interesting, but the question I am asking in this post is motivated by the latter kind of dispute.

To answer our question about where the bottom actually bottoms out consider what is implied by this latter kind of dispute. This possibility seems to imply the bottom is more generalizable and/or fundamental than previously proposed. It might even be committed to the idea that all phenomena bottom out in the same generalizable and/or fundamental stuff. If one if committed to this view (and it seems that many scientists are tacitly committed to this), then one will think that sciences should try to unify such that the phenomena studied in each science would be related to the generalizable and/or fundamental entities or forces at the bottom of everything. If sciences were thusly unified, then cognition and behavior would be explainable in terms of neuroscience and psychology, but also in terms of biology, chemistry, and physics.

Alas, we are a far cry from such a unified theory or the ability to understand such complex systems like the brain at such a fine-grained level of analysis. So for now, we treat cognition and behavior as if it bottoms out in the brain. This means that cognitive scientists take into account both coarse-grained data like behavior and neural events as well as finer-grained data like the biology and chemistry of neurons, but they do not take into account details so fine-grained as atomic particles.1

So it seems that we have an answer to our question. At least in practice, cognitive scientists seem to tacitly assume that “bottom up” will bottom out in the biological and chemical phenomena of the brain. What I have tried to suggest, however, is that the bottom is ultimately a moving target—one which depends largely upon scientists’ ability to unify various sciences and to understand increasingly complex systems.


  1. There have been attempts to explain consciousness in terms of fine-grained details from quantum mechanics, but such attempts are not taken seriously by the academic community.

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Nick Byrd

Nick is a cognitive scientist studying reasoning, wellbeing, and willpower. When he is not teaching, in the lab, writing, exercising, or relaxing, he is blogging at www.byrdnick.com/blog