In the first part of our triptych, we saw that the brain is not a passive decoder of the external world. It continuously maintains an internal model of reality, predicts what it should register, and corrects its own representation when a prediction error appears. But this opened a new question.
If an enormous number of signals pass through the nervous system at every moment, why are we conscious of only some of them?
As you read this sentence, your eyes are registering far more than the letters themselves. Peripheral vision is monitoring the surroundings, the skin is sensing the pressure of clothing, the inner ear is tracking head position, proprioceptive receptors are monitoring the position of the limbs, the auditory system is processing sounds in the room, and the autonomic nervous system is continuously monitoring the state of the internal organs. Most of this information is processed without any clear entry into consciousness.
Only when a signal becomes important enough — when we hear our own name, feel pain, notice movement in peripheral vision, or deliberately focus on our own breathing — does it seem to emerge from the background and enter the mental stage.
How does that happen?
Attention and Consciousness Are Not the Same
At first glance, it seems logical to say that we are conscious of whatever we pay attention to. But the relationship between attention and consciousness is more complicated than that.
A large part of attention can be automatic. A sudden bang, rapid movement, or change in light can attract our attention before we consciously decide to analyze it. Likewise, the nervous system can process certain information in detail without that information becoming part of our conscious experience.
That is why attention and consciousness should not be treated as identical. Attention is primarily a mechanism of selection and prioritization, while consciousness is the state in which a certain content becomes available to a wider range of brain processes — memory, decision-making, planning, verbal report, and intentional behavior.
In other words, attention can increase the probability that a signal will enter consciousness, but it is not itself the same thing as consciousness.
The Brain Does Not Have Enough Resources for Everything
One reason selection is necessary is that the nervous system has limited resources.
Sensory systems can process an enormous amount of information in parallel, but detailed analysis, comparison with memory, decision-making, and conscious planning have much more limited capacity. If every signal were given equal priority, the system would quickly become overwhelmed.
The brain therefore has to decide what is important at any given moment.
Some signals gain priority because of their physical salience. A loud sound, sudden movement, or pain automatically attracts attention. This is often called bottom-up (from the bottom upward) or stimulus-driven attention.
Other signals gain priority because we are actively searching for them. If we are expecting a friend at a railway station, a face that would otherwise be just one among hundreds suddenly becomes highly significant. This is top-down (from the top downward) attention — an internal goal changes the way we process sensory information.
Here we can already see the connection with predictive processing: the brain does not assess the importance of a signal only according to its amplitude, but also according to how well it fits our goals, expectations, and internal model of the world.
Neural Gain: When the Brain “Turns Up the Amplification”
In electrical engineering, the concept of gain is completely natural. One signal can be amplified relative to other signals, thereby increasing its influence on the next stage of the system.
Something functionally similar exists in the nervous system.
The term neural gain describes a change in the sensitivity of a neural network to a particular input. When gain increases, the same input can produce a stronger or more reliable neuronal response. The system does not need to create a new signal; it changes the weight assigned to an existing signal.
If, among ten simultaneous inputs, only one receives greater neural gain, that signal can have a much stronger influence on further processing. The others have not disappeared, but their functional importance becomes smaller.
From an engineering perspective, we might imagine a system with multiple input channels, each with variable gain. A control layer determines which channel will receive more amplification at a given moment.
In the brain, however, there is no single potentiometer for attention. Selection and amplification arise through the cooperation of several systems. Frontal and parietal cortical networks participate in deliberate attentional control, while the thalamus regulates the flow of a large part of sensory information toward the cerebral cortex. Thalamic structures such as the pulvinar nuclei are particularly important in coordinating visual attention and communication between cortical areas.
But the importance of information is not only a matter of sensory clarity. The brain must also assess the emotional and biological value of a signal.
This is where structures traditionally associated with the limbic system become important, including the anterior cingulate cortex, the insula, and the amygdala. The anterior cingulate cortex participates in evaluating conflict, error, and significance, while the insula links external events with the internal state of the organism. Together with other structures, they form part of networks that evaluate what is important enough, at a given moment, to deserve additional neural resources.
The amygdala has a particularly important role.
If the nervous system identifies a signal of potential danger, the amygdala can rapidly increase the priority of information related to that threat. Attention narrows, irrelevant information loses importance, and the system prepares for a fast response.
In an engineering analogy, the amygdala somewhat resembles an emergency-stop button.
Of course, it does not literally switch off higher brain functions. But under acute threat, it can strongly shift system priorities so that slower, analytical processing in the prefrontal cortex has less relative influence, while faster and evolutionarily older response patterns gain priority.
In a moment of panic, it is not important to analyze in detail the color of an object rapidly approaching our face.
What matters is getting out of the way.
Such a system clearly has evolutionary value. The price is that intense fear can narrow attention so much that a person misses information that would have been easily noticed in a calmer state.
Neural gain, therefore, is not merely “amplification of a signal.” It is part of a system that constantly decides what currently deserves the brain’s resources.
The “Spotlight”: A Reflector on the Mental Stage
One of the best-known metaphors of attention is the spotlight — a beam of light illuminating only one part of a much larger scene.
The scene exists outside the illuminated area, but what lies under the spotlight is processed in greater detail.
In visual attention, this can be demonstrated very easily. We can look straight ahead while mentally directing attention toward an object slightly off to the side. The eyes have not moved, the image on the retina has not changed, but the processing of that part of the visual field becomes more intense.
Attention, therefore, is not the same thing as moving the sensor.
It is a change in how the brain processes already existing information.
The spotlight metaphor is useful more broadly as well. Mental focus can shift from the external world toward internal processes: pain, a memory, a particular thought, or our own breathing. In each case, a particular set of signals gains privileged access to neural resources.
However, the spotlight should not be understood literally. There is no single center in the brain that “illuminates” content. Selection involves distributed networks, particularly frontal and parietal systems, the thalamus, structures that evaluate emotional significance, and various neuromodulatory mechanisms.
The “spotlight” is therefore a useful functional metaphor, not an anatomical description.
The Thalamus: More Than a Relay Station
In older simplified descriptions, the thalamus was often portrayed as a relay station that merely forwards sensory information to the cerebral cortex.
Today we know that its role is far more active.
The thalamus participates in regulating information flow between different brain regions and can influence which signals gain greater access to cortical networks. Its connections with the cortex are not one-way. The cortex sends extensive feedback projections back to the thalamus, creating complex thalamocortical loops.
It may therefore be more accurate to think of the thalamus not as a simple relay, but as a kind of dynamic router.
It does not decide by itself what will become conscious, but it participates in traffic management across the network. Here again, the analogy with computer systems is useful: it is not enough for a packet to reach the network. What matters is which nodes it passes through, what priority it receives, and which resources it can access.
The Chemistry That Decides What Matters
Changes in neural gain are not merely a consequence of the electrical activity of neural networks. Neuromodulatory systems also play an important role.
Acetylcholine, noradrenaline, dopamine, and other neuromodulators can change the sensitivity of large neuronal populations and thereby influence attention, arousal, motivation, and learning.
If a potential threat appears in the environment, the noradrenergic system can shift the state of entire neural networks so that the organism becomes more prepared to detect unexpected events. If we expect a reward, dopaminergic systems can change the significance of certain signals and behaviors.
In other words, the question “What are we conscious of?” does not depend only on what enters through the senses.
It also depends on the state of the brain receiving that signal.
The same sound can be completely irrelevant while we are sitting calmly at home and extremely significant if we hear it in the middle of the night in an unfamiliar place.
The signal is the same.
The system gain is not.
From a Local Signal to Global Access
This brings us to one of the most interesting questions in the science of consciousness: what happens when a signal stops being merely locally processed information and becomes part of conscious experience?
One influential theoretical framework is Global Workspace Theory, and its neurobiological version, the Global Neuronal Workspace. In very simplified form, the idea is that many processes in the brain can occur locally and unconsciously, but certain information becomes conscious when it gains access to a widely distributed network and becomes available to many other systems.
We can imagine this as a theater stage.
Dozens of processes are working simultaneously behind the scenes. The audience does not see most of them. But when a particular content comes under the spotlight and onto the central stage, it becomes available to the whole system.
Of course, this is not proof that we have discovered the final mechanism of consciousness. Global Workspace is one important theory, but competing models also exist. Still, the metaphor is useful because it connects attention, signal amplification, and wider information availability.
In engineering language, we could say that a particular signal moves from local processing onto the shared system bus.
From that point onward, it can be used by different modules: working memory, speech, planning, decision-making, and motor systems.
The Threshold of Consciousness May Not Be an Ordinary Threshold
The simplest model would be to assume that there is some signal amplitude below which we are not conscious and above which we become conscious.
But the nervous system probably does not work so simply.
A weak signal can become conscious if we expect it, actively search for it, or if it has great biological significance. On the other hand, a relatively strong signal can remain practically unnoticed if it is predictable and irrelevant.
A person living next to a railway line may stop consciously noticing passing trains, while a very quiet and unusual sound from the next room may wake them immediately.
The importance of a signal is therefore not determined only by its physical strength.
It is determined by amplitude, expectation, context, previous experience, emotional value, and the current state of the system.
In other words, the brain does not ask only:
“How strong is this signal?”
It also asks:
“How important is this signal?”
When We Amplify Our Own Pain
This mechanism can be seen very clearly in pain.
If we focus our attention on a particular painful sensation, the subjective intensity of the pain can often increase. If attention is strongly engaged by another activity, the same peripheral signal may be experienced as less intense.
That does not mean the pain is “imagined.”
On the contrary, it shows that pain is the result of complex processing in which the peripheral nociceptive signal is only one part of the system. The brain evaluates context, expectations, danger, previous experience, and emotional state, and then determines how strongly that signal should be emphasized.
This connects directly with the placebo and nocebo effects from the first part of the triptych. Expectation can change the gain of the system.
If we expect relief, pain processing can be reduced. If we expect worsening, the same signal can receive greater weight.
Prediction and amplification then become two sides of the same story.
What Happens When We Amplify the “Wrong” Signal?
Here we reach the boundary where this subject becomes especially interesting.
If the brain has mechanisms that selectively amplify certain signals, it is possible to imagine that sometimes amplification is assigned to a signal that would normally have little importance.
This can be harmless. In a quiet room, we may suddenly become aware of our own heartbeat or of the faint sound of a fan that we had previously ignored completely.
But the same principle can also have more serious consequences.
In some psychiatric and neurological conditions, the relationship between internal predictions, sensory signals, and their weighting may become disturbed. A weak or ambiguous signal may receive too much weight, while internally generated content may be interpreted as if it came from the external world.
This opens the question of hallucinations.
Does a hallucination occur because the brain creates a signal that does not exist, or because it assigns an internal signal the weight it would normally assign to an external one?
The answer is not simple, and different forms of hallucination probably do not share the same mechanism. But predictive processing and neural gain provide a very interesting framework for asking the question.
And What About Intuition and the “Sixth Sense”?
This is an area where we must be especially careful to distinguish what we know from what we merely hypothesize.
It is scientifically well established that the brain processes far more information than reaches conscious focus. Microexpressions, changes in voice, peripheral visual information, smells, bodily reactions, and statistical patterns of behavior can all influence our decisions before we are consciously able to explain why we have a certain feeling.
That is why a person may sometimes say, “Something is not right here,” and only later identify the signal that triggered the feeling.
This is a perfectly legitimate neurobiological basis for part of what we call intuition.
Much more speculative is the claim that the brain can detect physical signals for which we have no known sensory mechanism and then selectively amplify them to the level of consciousness. Such ideas do exist, but we currently do not have the same level of evidence for them that we have for classical sensory and attention-mediated processes.
Still, the fact that most neural processing remains outside awareness leaves an interesting space for investigation.
Perhaps we often register far more than we think.
But that does not mean we can reliably claim that we register what we have no evidence we are physiologically capable of detecting.
The Mental Spotlight
Our consciousness therefore may not resemble a control room in which all signals of the nervous system are visible at once.
It is more like a stage illuminated by a narrow spotlight.
Behind the stage and in the darkness, an enormous amount of processing is constantly taking place. Signals are compared, predicted, filtered, and placed in competition with one another. Most never enter the central space of conscious experience.
But some gain priority.
Their neural gain increases, broader networks become activated, and they become available to working memory, decision-making, speech, and intentional behavior. At that point, we say that we have become conscious of them.
In the first part of the triptych, we concluded that the brain does not decode the world, but continuously negotiates with it.
Now we can add another layer:
consciousness does not listen to all participants in those negotiations equally loudly.
Some get the microphone.
Others remain in the background.
And in the final part of the triptych, we will go one step further. What happens when the brain begins to produce content almost without an external interlocutor — when the spotlight illuminates what the brain itself has created?
That is where imagination, dreams, and creativity begin.
But hallucinations begin there as well.
And perhaps the most interesting boundary of all:
how do we distinguish the world we perceive from the world created by our own brain?
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