Consciousness is the awareness that we have of our own existence. It is the awareness of our sensations, thoughts, feelings, and the environment that surrounds us. Since at least the time of Aristotle, people have debated the meaning and origins of consciousness.
We can now study consciousness at the neural level. A popular belief is that some brain regions give rise to our conscious experiences, whereas other brain regions do not. For example, if the cerebellum is damaged, our consciousness remains relatively unaffected. Cerebellar patients can still see, hear, and feel just fine. They still retain a sense of self and can retrieve memories back into conscious awareness.
Damage to other brain regions can severely impair consciousness. For example, damage to the cerebral cortex can cause impairments in consciousness. For example, patients with strokes in the cerebral cortex can lose the ability to recognize items or understand language.
One distinguishing feature between the cerebellum and the cerebral cortex is their neural architecture. The cerebellum’s neural architecture can be construed as a relatively simple feed-forward circuit. One set of neurons feeds to the next, which, in turn, feeds to the next. In contrast, the cerebral cortex’s neural architecture contains many feed-forward and feed-back loops across networks of neurons.
Most consciousness theories hold that the complex architecture of the neurons situated within the cerebral cortex is an essential factor that helps give rise to consciousness. Some theories of consciousness make the additional assumption that different brain regions give rise to different conscious states. One such theory, the adaptive resonance theory (ART), is featured in a recent paper by Stephen Grossberg (pictured below) published in Psychonomic Society’s journal Attention, Perception, & Psychophysics.
Grossberg proposed ART to solve a problem he calls the “stability-plasticity dilemma.” In a complex and ever-changing world, we are bombarded by vast amounts of information. To survive, we need to sift through that information quickly without forgetting what has already been learned. Grossberg explains that resonant states solve this problem.
A resonant state occurs when neurons across a brain network rapidly fire together in synchrony. For example, what we see, hear, and feel through our senses is information that enters our cognitive system in a bottom-up process. This information can activate expectations retrieved in a top-down process from long-term memory. When sensory information and expectations match, they amplify each other and form a resonant state. If that resonant state is strong enough and lasts long enough, it achieves consciousness.
According to ART, various brain networks give rise to different resonant states. One type of resonant state is feature-category resonance. This resonant state is the product of the “what” cortical stream. This stream travels from the occipital lobe to the temporal lobe. The bottom-up visual information that enters this stream is the object’s features, such as its color, shape, and texture. This information activates expectations retrieved from long-term memory about what the object could be. If these bottom-up and top-down processes match, then a feature-category resonance occurs. When the feature-category resonance occurs, we have the conscious experience of object recognition.
Another type of resonant state is surface-shroud resonance. This resonant state is the product of the “where” cortical stream. This network helps determine an object’s location, and when the surface-shroud resonance occurs, we consciously appreciate the object’s location.
Together, the “what” and “where” streams complement each other to allow us to recognize, locate, and interact with objects. The figure below illustrates these two cortical streams and the two types of resonant states that they produce.
According to ART, without these resonant states and the linked conscious experiences, the ability to interact with objects is impaired. Consider, for example, when one cortical stream is damaged, but not the other. Patient D.F. had neurological damage to the “what” cortical stream. Unsurprisingly, this neurological condition had a severe impact on D.F. For example, when scientists placed a letterbox in front of her, she could not accurately describe or draw the object. There was nothing wrong with her eyesight. Instead, she was unable to consciously “know” what objects were in front of her.
Yet, when scientists asked D.F. to insert a card into the letterbox, she did so with remarkable accuracy and precision. How was this possible?
Grossberg explains that D.F.’s neurological damage likely impaired the formation of the feature-category resonant state, which explains why D.F. no longer had conscious awareness of the types of objects in her environment. Even though D.F. could not recognize the object in front of her, she could still insert a letter into the box presumably because the “where” cortical stream was still intact. In this sense, D.F. could still “see” the box even though she did not “know” what it was. The figure below illustrates this effect.
According to ART, the consciousness that arises from various resonant states is necessary for successful behaviors (such as interacting with a letterbox). However, ART predicts that not every resonant state gives rise to consciousness. For example, resonant states that are not accessible to consciousness include the entorhinal-hippocampal resonances that stabilize the learning of entorhinal grid cells and hippocampal place cells and the parietal-prefrontal resonances that help control contextually-appropriate thought and action. According to ART, these resonances do not give rise to consciousness because they are not activated by external senses, such as sight and sound, or internal senses, such as emotion, that enter our cognitive system through bottom-up processes.
ART is a bold theory that attempts to explain the reason why our brains developed consciousness. Although we as human beings have investigated the mysteries of consciousness for centuries, psychological science and neuroscience help to get us closer to solving that mystery.
Psychonomics article featured in this post:
Grossberg, S. (2019). The resonant brain: How attentive conscious seeing regulates action sequences that interact with attentive cognitive learning, recognition, and prediction. Attention, Perception, & Psychophysics, 81, 2237-2264. https://doi.org/10.3758/s13414-019-01789-2
