I’ve noticed a tendency to view the the nervous system and what it does in a kind of black box that receives input from and responds with output to the environment. Input is generally the sensory systems like vision, hearing, smell, taste, and touch. While output is mostly movements expressed through the motor system (and if you’re a octopus or a cuttlefish then through changing of skin pigmentation too). In general, the picture looks like this:
In other words, the environment sends input to the brain, “something” happens there, and the organism responds with some output.
But this picture could be expanded to include a similar, symmetric behavior of the environment, into something like this:
Here, something happens in the environment, it becomes transformed as input to the brain, where further something happens, that then get’s transformed as output, and in turn, affects the environment. That middle part is the environment-nervous system interface that looks something like this:
In this picture, the environment is separated from the neural system via an interface between the two. The interface is clear and well defined: it defines where the environment ends and neural system begins.
But the idea of a clear, well defined interface, while conveniently keeps environmental and neural concerns separate, artificially limits a more accurate picture of the two.
From physics, we know that things get fuzzy on small scales, and this fuzziness only allows for fuzzy, artificial boundaries. Just like there is no clear boundary where an atom begins or ends, there is no clear boundary between an organism and its environment. If the mental boundary is erased, the following picture emerges:
Here, the environment forms one dynamic system, which is coupled to another dynamic system, the brain. These two systems are only loosely coupled, in the sense that only a small portion of what happens inside each system has an effect on the other. This also implies that the two systems operate individually on shorter time scales and exchange information on larger scales.
The more accurate picture is then to view the brain and environment as one system composed of loosely-coupled sub-systems with no clear separation between the two.