A cortical atlas of ghostly sensations

Frontiers in Neuroscience has an amazing scientific article that has collected all the studies that have recorded what happens when the brain is electrically stimulated in living patients. It’s like a travel guide to the unnaturally active brain.

As you might expect, science generally takes a dim view of researchers cracking open people’s skulls just to see what happens when bits of their brain are stimulated, hence, almost all of these studies have been done on patients who are undergoing brain surgery but have agreed to spend a few minutes during the operation to report their experiences for the benefit of neuroscience.

This procedure is also essential in some forms of brain surgery to make sure the surgeons avoid essential areas. For example, in some cases of otherwise untreatable epilepsy the surgeons track down the ‘foci’ or trigger area, and can often stop seizures completely just by removing it.

However, if an area is heavily involved in speech production, you wouldn’t necessarily want to give up being able to talk for the sake of being seizure free, so surgeons will open the skull, wake you up, and then ask you to speak while stimulating the areas they are considering removing. They can map your speech areas by seeing when you can’t speak as the areas are stimulated, and hence, know what areas to avoid.

So through years of experimental and clinical studies we now have what amounts to a travelogue of what happens when brain areas are stimulated. Neuroscientists Aslihan Selimbeyoglu and Josef Parvizi have compiled these reports into something like a cortical guidebook.

Here’s the entry for the temporal lobe:

Stimulations in the anterior medial temporal structures were associated with complex feelings and illusions such as feeling of unreality or familiarity (déjà vu) or illusion of dream-like state; emotional feelings such as feeling of loneliness, fear, urge to cry, anger, anxiety, levitation, or lightness; and recall of past experiences.

Stimulations in the superior temporal structures were associated with hallucinations in the auditory domain such as hearing “water dripping”, “hammer and nail”, music, or human voices, or changes in the quality of auditory stimuli such as muffling of environment. If stimulations of the superior temporal region were in the depth of the sylvian fissure, and toward the insula, stimulations induced pain or automatisms such as sudden movement, staring, unresponsiveness, plucking, or chewing.

Stimulations in the inferior and middle temporal and temporooccipital structures were associated with hallucinations in the visual domain such as seeing a face, geometric shapes, and color or blurring of vision, macropsia, visual movement, things looking sideways, and lines seeming out of kilter. In addition, disruption in reading, or reading comprehension, picture naming and or identification were also reported with left inferior temporal lobe stimulations. Laughter with a sensation of mirth was associated with stimulation of the left inferior temporal region in the vicinity of the parahippocampal gyrus.

The article is open-access so you can read the full details online.

Link to ‘Electrical stimulation of the human brain’.
Link to so-so Wikipedia page on ‘When Prophecy Fails’.