The free choice whether or not to respond after stimulus presentation

Abstract

The concept of 'willed' actions has attracted attention during the last few years. Free choices have been associated with activations on the medial frontal surface, the dorsolateral prefrontal cortex and the parietal lobe. Self-paced movements and free selection between various motor responses were typically used to investigate voluntary behavior. The aim of the present study was to determine neural correlates of voluntary motor responses and the voluntary inhibition of motor responses in a group of healthy subjects. Hence, a go/nogo/voluntary selection paradigm was used. In the voluntary selection condition subjects decided freely whether or not to respond with a button press after stimulus presentation. Functional MRI data and event-related potentials were acquired simultaneously in order to reliably investigate spatial and temporal characteristics of these responses. The results showed decision-related enhanced neural responses predominantly in the medial frontal gyrus/supplementary motor area, lateral frontal brain regions and the inferior parietal gyrus. Additional activations associated with voluntary movements were detected in the frontal eye field as well as brain regions directly linked to motor responses (e.g. somatosensory cortical areas). Altogether, decision processes were shown to be relatively independent of the kind of response chosen.

Figure 1

Auditory go/nogo/voluntary selection paradigm.

Figure 2

Behavioral data. Boxplots show mean response time [A] and percentage responses [B] for go and voluntary selection trials. Asterisks indicate level of significance: ***p < .001; **p < .01.

Figure 3

ERP waveform during go, nogo and voluntary selection condition at frontal and central electrode positions.

Figure 4

ERP waveform during voluntary selection without behavioural response [selection‐] compared to the selection to respond with a button press [selection+] at frontal and central electrode positions.

Figure 5

Correlation between P₃‐amplitudes [μV] of FCz, Cz and Pz and the corresponding reaction times [ms] for the selection+ and go task.

Figure 6

Functional MRI responses to the voluntary selection task compared to the control condition (random effects analysis thresholded at p(uncor) < .001; confidence range T: 4.3⁻⁸; xyz: 0 10 40). [Abbreviations: sfG: superior frontal gyrus, mfG: medial frontal gyrus, cG: cingulate gyrus, Pre: Precuneus; mdfG: middle frontal gyrus; ipG: inferior parietal gyrus]. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 7

Functional MRI responses to the voluntary selection task without behavioural response [selection‐] compared to the nogo condition and the voluntary selection with behavioural response [selection+] compared to the go condition, respectively (random effects analysis thresholded at p(uncor) < .001; confidence range T: 4.3⁻⁸; xyz: 4 22 44). [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 8

Brain responses associated with voluntary behaviour compared to forced behaviour (factorial analysis (“voluntariness” and “response”); random effects analysis thresholded at p(uncor) < .001; confidence range T: 4.3⁻⁸). [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]