On the role of the prefrontal cortex in fatigue effects on cognitive flexibility - a system neurophysiological approach

Figure 1. Reaction times (RTs) in milliseconds in the three experimental blocks (block 1 till block 3). The means and standard errors of the different experimental conditions “cue repetition” (diamond), “cue switch” (square), “memory repetition” (triangle), and “memory switch” (circle) are shown.

Figure 2. Event-related potential (ERP) components in the cue-based (left) and memory-based (right) condition. (A) The P1 (~100 to 110 ms) and N1 (~150 to 160 ms) ERP-components are shown for electrode P7 and P8. The N2 ERP-component at electrode Cz is shown in (B). The P3 ERP-component (~320 to 460 ms) is shown at electrodes P3 and P4 (C). Time point zero denotes the time point of target stimulus presentation. Additionally, scalp topographies of repetition versus switch trials of the two different experimental conditions are shown at the maximum peak for respective ERPs. In the topographies, positivity is shown in red and negativity in blue.

Figure 3. The S-cluster and C-cluster from the RIDE analyses are presented for the cue-based (left) and memory-based (right) condition. The S-cluster (top) reflects activity in the P1 (~100 to 110 ms) and N1 (~150 to 160 ms) time window at electrode P7 and P8. The C-cluster reflects activity in the N2 time window at electrode FCz (middle part of the figure) in the cue-based trials (left) and the memory-based trials (right). Moreover, the activity in the P3 time window was evident (lower part of the figure). Scalp topographies of the four different experimental conditions are included, showing the respective RIDE topography at the maximum of respective peaks in the different time windows. In the topographies, positivity is shown in red and negativity in blue.

Figure 4. The R-cluster from the RIDE analyses is presented. (A) The R-cluster shows activity in the P3 time window at electrodes P4 and PO2 for the cue-based (upper part) and memory-based trials (lower part). As our behavioral results showed that switch costs (switching minus repeating trials) were modulated over time (experimental blocks), the switch costs (i.e. differences between the first and third block) are shown separately for cue-based trials (blue) and memory-based trials (red). Significant modulations of switch costs were shown only in the memory-based trials. Topographies for the differences between the first and third block at the maximum peak are shown for the memory-based trials in the upper part of the figure and for cued trials in the lower part of the figure. In the topographies, positivity is shown in red and negativity in blue. The difference in switch costs between the tasks (memory-based minus cued trials) is presented in green including the all-in-one scalp topography plot. Time point zero denotes the time point of target stimulus presentation. The sLORETA results show the source of the neurophysiological signal in this time range in BA10 (corrected for multiple…

Figure 5. Schematic illustration of the cue-based (upper part) and the memory-based task switch paradigm (lower part). The cue-based task is initiated by one of three explicit task rules (in this example “GER” (German for “Geradzahligkeit”), asking for the parity of the upcoming digit). The cue is followed by the presentation of one of eight possible digits (“1” to “9”, without “5”). Then, a response had to be given in within 500 ms with the left or right control key of a standard keyboard. After that, a feedback (“+” or “−”) was given for 500 ms until the next trial started. In the memory-based condition, the procedure of one trial was identical, except of the presentation of the task cue, which was replaced by an uninformative cue (“XXX”). Here, a fixed trial order had to be recalled, which included all three explicit task cues (AAA, BBB, CCC).