We have written here about both magnetic and transcranial direct current non invasive stimulation of the motor cortex for central pain. Here is an expansion on the idea.
Fregni et al from Harvard have published in Lancet Neurol. 2007 Feb;6(2):188-91, an article entitled, “Recent advances in the treatment of chronic pain with non-invasive brain stimulation techniques.”
The authors report experience in the department of Neurology at Harvard. Significantly they are not just treating central pain but also visceral pain (pain in the hollow organs of the body).
They relate attempts to vary the experience in order to improve the effectiveness of both magnetic and direct current stimulation. One area of experimentation involves extending the area of stimulation from the motor cortex (MI) and primary somatosensory cortex (SI) to the “secondary somatosensory cortex (ie. SII in the parietal lobe rather than primary motor cortex or SI located respectively in front of and in back of the central sulcus of the brain) for the treatment of chronic visceral pain and new parameters of stimulation, such as repeated sessions of tDCS with 2 mA for the treatment of chronic central pain”.
The authors also indicate “Other parameters of stimulation need to be further explored such as theta-burst stimulation** and the combination of tDCS and rTMS.”
In a very forward looking stance, they are conceiving of ways the treatment might be continued, inviting us to regard transcranial treatment not as a one time shot but possibly as more or a maintenance therapy. Somehow it seems comforting to think of brain stimulation as more like TENS than mind altering shocks. We are glad to see this thing being fleshed out and hope it brings results.
Theta burst stimulation refers to a type of waveform which mimics signalling in the awake hippocampus. Most study of theta burst stim comes from research on memory. For example, see Nguyen et al Learn Mem. 1997 Jul-Aug;4(2):230-43. “Brief theta-burst stimulation induces a transcription-dependent late phase of LTP requiring cAMP in area CA1 of the mouse hippocampus”.
The Howard Hughes Institute at Columbia in New York has concluded that “memory storage in the mammalian brain can be divided into a short-term phase that is independent of new protein synthesis and a long-term phase that requires synthesis of new RNA and proteins.”
During exploratory behavior in awake animals, a type of brain wave known as “theta” is seen in excitation pathways in the hippocampus. Theta activity results in long term potentiation, or heightened responses at nerve synapses over a drawn out period of time. Tetanus is an extreme form of long term potentiation but there are lesser varieties. It is not absolutely clear that spontaneous dysesthetic burning of central pain is not the sensory equivalent of tetanic muscle contractions. There is no research indicating theta bursts are related to pain. However, it is known that theta LTP requires NMDA, which is a pain exciter. However, the speculation that theta burst stim would help pain is at this point quite a reach. However, the late stage of theta LTP is blocked by inhibitors or protein kinase A, a known pain chemical. Therefore, it is encouraging to see the above scientists thinking along all lines, hoping for a breakthrough.