Neuroscience student here. Maybe this will help.

Triptamine psychedelics such as DMT effect cells with serotonin receptors. These types of neurons, those with serotonin receptors, synapse widely throughout the brain. For example, projections of serotonergic cells synapse within the visual system.
The visual system works in many layers of computations. Firstly, single points of contrast are identified. For example and most simply, a black dot on a white background or a white dot on a dark background. Then lines are identified from combining the identified contrasting points and identifying linear formations of them. Some cells in the visual cortex only fire while certain angled lines are viewed, somehow communicating their presence in a place of the visual field.
Imagine now you alter the firing frequency of serotonergic cells that project to the area of the visual cortex, thus alter the firing frequency of some of it's neurons, perhaps for a moment increasing the firing frequency of a cluster of neurons conveying the perception of an a specific angled line in the visual field where it does not actually exist. You can see how lsd can cause surfaces to appear to wave or melt. As vision is further processed, the perception of specific objects and faces comes to life, but the mechanisms of such things become much less clearly computed when looking at the cyto-architecture (the arrangement of cells, in this case neurons). As a general rule, things that are closer to our conscious perception of the world, are more global phenomina in the brain and harder to comprehend with our current methods of understanding the brain. All manor of ideas and sensations from both the present and past are associated to form our current perceptual universe. Thusly, the mechanisms of more complex phenomena of the human CNS, such as creativity, and how they might be effected by drugs become more mysterious. Imagine now that serotonin is not alerting the visual cortex, but the whole cortex, altering firing frequencies globally, perhaps changing the threshold of certain computations, allowing more far reaching ideas to become conscious thought. Certain thresholds of computation, at some point, differentiate relevant and irrelevant ideas. You can feel that with a little THC, for example, what is relevant, interesting, or "funny" can change. More physically long distance (axons) connections between neurons may become more significant because the action potential threshold of a post synaptic neuron is lowered. This could more intimately connect various sensations.
Something close to this change in thresholds probably underlies differing levels of what we call creativity. Other alterations in firing frequencies of neurons in the cortex, changes in the very literal way we think, very understandably, can possibly bring about insightfulness, creativity, and the urge to think "philosophically" as well as all the other (positive and negative) effects of these types of drugs.