I’ve had a number of conversations lately on the subject of feelings, the affective states of having valences about conscious perception, such as fear, pain, joy, hunger, etc. Apparently a lot of people view feelings as a very mysterious phenomenon. While I’ll definitely agree that there are a lot of details still to be worked out, I don’t see the overall mechanism as that mysterious. But maybe I’m missing something. Along those lines, this post is to express my understanding of mental feelings and give my online friends a chance to point out where maybe I’m being overconfident in that understanding.
To begin with, I think we have to step back and look at the evolutionary history of nervous systems. The earliest nervous systems were little more than diffuse nerve nets. Within this framework, a sensory neuron has a more or less direct connection to a motor neuron. So sensory signal A leads to action A. No cognition here, no feelings, just simple reflex action. The only learning that can happen is by classical conditioning, where the precise behavior of the neural firings can be modified according to more or less algorithmic patterns.
As time went on, animals evolved a central nerve cord running along their center. This was the precursor to the vertebrate spinal cord. All (or most) of the sensory neural circuits went to this central cord, and all (or most) of the motor circuits came from it. This centralization allowed for more sophisticated reflexes. Now the fact that sensory signal A was concurrent with sensory signal B could be taken into account, leading to action AB. This is still a reflex system, but a more sophisticated one.
As more time went on, animals started to evolve sense organs, such as a light sensing photoreceptor cell, or sensory neurons that could react to certain chemicals. These senses were more adaptive if they were in the front side of the animal. To process the signals from these senses, the central trunk started to swell near the front, becoming the precursor to a brain.
The new senses and processing centers would still initially have been reflexive, but as the senses started to have more resolution to them, it allowed the nascent brain to start making predictions about future sensory input. These predictions expanded the scope of what the reflexes could react to. A mental image of an object, a perception, is a prediction about that object, whether it is a predator, food, or irrelevant to the reflexes.
Up to this point, there are still no feelings, no affects, no emotions, just sensory predictions coupled to a more or less algorithmic reflex system. This is where many autonomic robots are today, such as self driving cars: systems that build predictive maps of the environment, but are still tied to rules based actions. (Although the organic systems were still able to undergo classical conditioning, something technological systems likely won’t have for quite a while.)
But with the ever higher volume of information coming in, the animal’s nervous system would increasingly have encountered dilemmas, situations where the many incoming sensory signals or perceptions led to multiple reflexes, perhaps contradictory ones. An example I’ve used before is a fish sees two objects near each other. One is predicted to be food, triggering the reflex to approach and consume it, but the other is predicted to be a predator, triggering the flight reflex.
The fish needs to ability to resolve the dilemma, to make predictions about what would happen if it approaches the food versus what would happen if it flees, and what its reflexive reactions would be after each scenario. In other words, it needs imagination. To do this, it needs to receive the information on which reflexes are currently being triggered.
Consider what is happening here. A reflex, or series of reflexes, are being triggered, and the fact of each reflex’s firing is being communicated to a system (sub-system, whatever) that will make predictions and then allow some of the reflexes to fire and inhibit others. In the process, this imaginative sub-system will make predictions for each action scenario, each of which will themselves trigger more reflexes, although with less intensity since these are simulations rather than a real-time sensory event.
This sub-system, which we could call the action planner, or perhaps the executive center, is receiving communication about reflexive reactions. It is this communication that we call “feelings”. So, feelings have two components, the initial reflex, and the perception of that reflex by the system which has the capability to allow or override it.
In other words, (at the risk of sounding seedy) feelings involve the felt and the feeler. The felt is the reflex, or more accurately the signal produced by the reflex. The feeler is the portion of the brain which evaluates reflexive reactions to decide which should be allowed and which inhibited. In my mind, the reflex by itself is not the feeling. It’s a survival circuit that requires separate circuitry to interpret and interact with it to produce the feeling.
In vertebrates, the brain is usually separated into three broad regions: the hindbrain, the midbrain, and the forebrain. The hindbrain, equivalent to the lower brainstem in humans, generally handles autonomic functions such as heartbeat, breathing, etc. The midbrain, often referred to as the upper brainstem in humans, is where the survival circuits, the reflexes that are in the brain rather than the spinal cord, typically reside. And the forebrain, equivalent to the cerebrum in mammals, is where the action planner, the executive resides, and therefore where feelings happen.
(Many people are under the impression that prior to mammals and birds, there wasn’t a forebrain, but this is misconception. Forebrains go back to the earliest vertebrates in the Cambrian Explosion. It is accurate to say that the forebrain structure is far larger and more elaborate in mammals and birds than it is in fish and amphibians.)
On feelings being in the forebrain, this is the view of most neurobiologists. There is a minority which question this view, arguing that there may be primordial feelings in the midbrain, but the evidence they typically cite strikes me as evidence for the reflexes, not the feelings. A decerebrated animal shows no signs of imagination, of having functionality that can use feelings, only of the reflexes.
So, that’s my understanding of feelings. My question is, what makes feelings a mystery? If you saw them as a mystery before reading this post and still do, what about them am I missing?
Edited per suggestions in the comments, changing references to “sensations” to “sensory signals” to clear up possible confusion. MS