Are the images in our heads physical? I can think of a banana in my mind, and I can see it, it's there, but it's not really there at the same time. It doesn't feel physical, but for me to be able to see it, it must be physical, right? Are the images just a collection of neurons firing?
Question: Are the images just a collection of neurons firing?

Answer: Evidence from clinical neurology and cognitive neuroscience at present shows that all mental activities, not just the image of a banana, occur from neural firings. Without neural firings, no mental activities can occur. What’s more, when the neural firings change, the mental activities invariably change accordingly. That’s why mental activities change whenever neural firings change because of diseases affecting their neural circuits (stroke, trauma, tumor, encephalitis, hypoglycemia, migraine aura, epileptic activity, neurotransmission-interfering drugs, etc.) or because of electrical or magnetic stimulation to the neural circuits. There has never been a scientific report documenting a mental activity occurring by itself without neural firings.

Now, one can postulate that a mental image is something that occurs separately and additionally to the neural firing or one can postulate that a mental image is something that occurs inherently in the neural firing without any additional entity occurring. At present, I think there is no consensus on this yet. But, in my opinion, I favor the second case as some authors do. For example, Moutoussis K (ref 1): “… a specific brain–activation pattern, leading to the formation of a specific percept. …  specific, individual perceptual experiences are caused by specific, individual brain activation pattern …”, Roederer JG (ref 2): “when does a specific distribution of neural firings actually become a mental image? This neural activity distribution does not become anything – it is the image.”, and Ukachoke C (ref 3): “…a mental process is the information-processing process, which is an entity that functionally occurs intrinsically in the physical neural process, not an additional entity that occurs separately from the neural process…”. (If you’re interested in more detailed discussion, you can read ref 3; I think it provides a good, systematic, and evidence-based argument for the case.)

Question: It (the mental image of banana) doesn't feel physical, but for me to be able to see it, it must be physical, right? Are the images in our heads physical?

Answer: This, the mental image of banana, is an interesting phenomenon that’s baffled philosophers, neuroscientists, and others who ponder over it for a long time. It (the mental image of banana) and other similar phenomena, such as the sound of the note C, the odor of the rose, and the feeling of a pinprick, that occur in our minds are called qualia [ref 4, ref 5, ref 6, ref 7]. Each has unique phenomenal characteristics that cannot be described by other phenomena and has to be experienced directly to know what it is like: what the mental image of banana is like, what the sound of the note C is like, what the odor of the rose is like, etc. (You never can describe these phenomena to anyone who has never had experiences of similar kinds of phenomena before, such as, you never can describe what the color red is like to the congenitally blind person, etc.) Again, at present, I don’t think there is a consensus on what qualia are. So, whether they are physical phenomena or not are still unsettled.

However, some author argues that qualia are physical phenomena and actually are just special kinds of information in the nervous system that neural circuits use to communicate some special information among them. These special kinds of information can occur from neural firings in some special ways. Because neurons are firing in some special ways, special kinds of information with those baffling phenomenal characteristics (vision, sound, odor, etc. in our mind) can occur. This is how qualia (including the mental image of banana) occur in the brain. If this is the case and if we count information as a physical entity, then qualia are physical entities. But they are not conventional physical entities like mass, energy, or force, because they are a different kind of physical entities – they are information entities. That’s why they (including the mental image of banana) don’t feel physical to you. (If you’re interested in more detailed discussion, you can read this article (ref 8))

References.


Moutoussis K. The machine behind the stage: A neurobiological approach toward theoretical issues of sensory perception. Front Psychol. 2016;7:1357. 
Roederer JG. Pragmatic information in biology and physics. Philos Trans A Math Phys Eng Sci. 2016 Mar 13;374(2063). PII: 20150152. 
Ukachoke C. Theorem II: The Mind is the Composite of All Information-processing Processes of the Brain. In: The Basic Theory of the Mind. 1st ed, 2018. Bangkok, Thailand.
Kanai R, Tsuchiya N. Qualia. Current Biology. 2012 May;22(10):392–396. 
Tye M. Qualia. Zalta EN, editor. The Stanford Encyclopedia of Philosophy.
Kind A. Qualia. Internet Encyclopedia of Philosophy. 
Qualia. Wikipedia. 
Ukachoke C. Chapter 3 – Qualia, Conscious Awareness, and Conscious Experiences. In: The Basic Theory of the Mind. 1st ed, 2018. Bangkok, Thailand.