by April Irwin
Each of the three experiments involved an image of a clock with a hand that begins rotating when the participant presses the enter key. They are asked to watch the center of the clock and then press a certain button with one of their index fingers (the finger that they used depends on the experiment). When they pressed the button, the clock hand stopped and they had to make a time judgement, which changed according to each condition and experiment. In some conditions, an audio tone placed before the clock hand was stopped, but in other conditions, the tone was played when a button was pressed. Before the clock-task, each participant had a 25-minute session with tDCS and the setup of the anodal (increases neuron excitability) and cathodal (decreases neuron excitability) electrodes changed according to the aim of the experiment.
The experimental design for this paper was extremely detailed, which is really wonderful if you’re attempting to replicate it. However, I want to explain that the electrodes were set-up according to fMRI studies with sense of agency with the goal of understanding how sense of agency may be distributed across the frontal (where the DLPFC is) and parietal (the location of the AG) lobes as well as how sense of agency is distributed across the hemispheres. Placing the electrodes at these places allows us to determine whether the AG or DLPFC have a large role in sense of agency.
I have presented the experimental conditions under which people were asked to demonstrate sense of agency, which may have positive implications on how we talk about it in neuroanthropology because knowing how things are being measured in labs may allow us to elaborate on those procedures and compare those to events in people’s real lives where they exhibit sense of agency. Now I will present the major findings from these experiments because that’s where the discussion usually begins. Also, what I’m appreciating about the authors that we’ve read thus far is their ability to take these findings and apply them to the concepts that they are studying.
Compared to the sham conditions where there was actually no stimulation, anodal stimulation of the left AG significantly reduced the likelihood that the audio tone was bound to keypress. This aligns with other studies that suggests that, “the AG processes mismatches in action outcomes” (Khalighinejad & Haggard, 2015, p. 100). The cathodal results from all three experiments supported that this type of stimulation tends to have weak effects on cognitive tasks. Their main conclusion is that this study provides a half-step forward and that more research will have to be done in order to make any definite conclusions. My big takeaway from this article is that both this experimental data and the theoretical discussions are needed in order to really move things forward.
Reference: Khalighinejad, N., & Haggard, P. (2015). Modulating human sense of agency with non-invasive brain stimulation. Cortex, 69, 93–103. http://doi.org/10.1016/j.cortex.2015.04.015