Damian K. F. Pang :
The human brain has been described as the most complex structure in the universe (Dolan, 2007; see also Pang, 2023).
Researchers estimate that we have over 100 trillion connections between the 86 billion neurons that make up our brain (Azevedo et al., 2009; Caruso, 2023).
Each of these connections can function as a logic gate, giving our brains computing power that far exceeds current supercomputers despite being a fraction of the size and requiring as little power as a lightbulb (Jorgensen, 2022), a million times less than current supercomputers (Madhavan, 2023).
In terms of raw computing power, estimates for our brains range from 1018 to 1025 FLOPS (Sandberg & Bostrom, 2008) compared to current supercomputer records of 4.42×1017 FLOPS (IBM, n.d.). Does this mean that the brain is simply a highly efficient supercomputer? If so, could we-in theory-replace it with silicon chips? I suggest that there are a few problems with this view.
While synapses between neurons can act as logic gates, it is important not to lose sight of the neurons themselves.
Like every cell in our body, neurons have incredible structures and biological machines inside them: Microtubules act as a scaffold or skeleton that provides shape and stability, mitochondria turn nutrients into usable energy, factories produce proteins, and much more (Bear et al., 2020).
This incredible complexity is hard to untangle and there is much we still don’t understand-from specific intracellular mechanisms to system-wide functions across the brain.
Nobel laureate Roger Penrose and anaesthesiologist Stuart Hameroff have suggested that quantum effects in microtubules are responsible for consciousness (Hameroff & Penrose, 1996).
While this theory is not widely accepted (Orf, 2024) it survives (at least on the fringes) because we are only just beginning to understand quantum effects in biological systems.
Given this incredible complexity and the many unknowns, it may be premature to suggest that the brain’s main function is solely computational. This may come close to an argument from ignorance.
It is entirely possible that all this complexity is simply there to support computation, much like a computer has things like a cooling fan or a battery.
However, dismissing anything non-computational as merely a support system may make us miss crucial elements: For a long time, the non-protein coding parts of DNA had been dismissed as junk DNA.
More recent findings suggest that these parts play a central role in gene expression and disease (Welsh, 2023).
The metaphor of the brain as a computer also breaks down in areas we do fully understand. Computation is the transformation of an input into an output based on specific rules (see Piccinini & Maley, 2021).
While this can be applied to a lot of things and while our computers are concrete, physical objects, we normally talk of computation as information processing, which is abstract and substrate independent (a universal Turing machine can be implemented in many ways, Piccini & Maley, 2021).
Here is where we run into problems because the brain does not just process abstract information but performs concrete functions that have effects across the body.
One example is the endocrine system: The brain interacts with different systems in the body through hormones and is involved in regulating their production and secretion (McEwen, 1999).
Crucially, the brain itself changes in response to environmental changes and hormonal feedback, including changing gene expression by adding chemical markers onto DNA and altering key functional structures within individual neurons (McEwen, 1999).
These functions are very much substrate dependent. While all of this could be simulated in a computer, the body cannot function on abstract information just as simulating nutrients will not alleviate hunger.
The inputs the brain receives come from specialised sensory receptors and a large part of the outputs control organs and tissues, like muscles. Here again, implementation and substrate matter.
The author is a researcher.
