What neural intervention shows
Altering brain activity can alter a specific experience. That establishes a causal role for neural processes while leaving the ultimate nature of experience disputed.
Changing a neural process and observing a corresponding change in experience provides stronger evidence than finding that the two vary together. An intervention helps identify a causal contribution. Its philosophical reach still depends on what the intervention actually establishes.
In a 2012 study, Parvizi and colleagues used electrical stimulation in a patient undergoing evaluation for epilepsy. Stimulating face-selective regions of the right fusiform gyrus distorted the patient’s conscious perception of faces. The result supports a causal contribution of those regions to that aspect of visual experience. A finding from one patient and a specific perceptual manipulation does not establish a complete account of consciousness.
The important inference concerns participation. Those neural processes are involved in determining how a face appears to this observer. Calling all brain evidence “mere correlation” misses the additional force of an intervention. It also obscures the work any alternative theory would have to do.
A filter theory, for instance, can propose that the affected processes regulate access to an independently existing consciousness. That proposal remains compatible with the observation at a broad level. Compatibility alone does not show that filtering is the best explanation. It would have to specify how the proposed filter yields this particular distortion, and what evidence could distinguish its account from local neural production.
Conversely, establishing a causal contribution does not by itself identify experience with the neural event. A process can be necessary to an occurrence without exhausting its nature. The philosophical issue requires an account of the connection between neural activity and felt appearance.
Two facts can therefore be held together without weakening either: the brain has experimentally supported causal involvement in the character of experience, and that involvement leaves disputed questions about what experience fundamentally is. A serious theory must accommodate both.
Within an eternalist history, the intervention and its perceptual consequence would be events with temporal locations. Their inclusion in a complete record leaves their causal relationship intact. A fixed history does not turn an experimentally effective intervention into an empty gesture.