Figure 2. Functional gradients along the rostro-caudal axis.

a | Summary of experimental findings from functional MRI (fMRI) studies and monkey electrophyiology along the rostro-caudal gradient. Across studies, there seems to be a trend for more-rostral regions to support more-abstract action rules. Anatomical locations of effects are approximate. b | Comparison of results from two fMRI studies showing functional gradients along the rostro-caudal axis of the human frontal lobe. Explicitly testing a rostro-caudal functional gradient, Koechlin et al.¹⁹ (shown in blue) and Badre et al.¹⁶ (shown in red) demonstrated highly convergent activation along a dorsal gradient from dorsal premotor cortex (PMd) (a,b; ~BA 6) to prePMd (c,d; ~BA 8) to mid-dorsolateral prefrontal cortex (PFC) (e,f; ~BA 9/46) to frontopolar cortex (g; ~BA 10), as cognitive control was required at progressively abstract levels. Although different forms of abstraction were tested — temporal abstraction in Koechlin et al.¹⁹ and policy abstraction in Badre et al.¹⁶ (see BOX 1) — the activation patterns observed in these two experiments were highly convergent. c | Race et al.¹¹³ aimed to locate a gradient of abstraction along the ventrolateral PFC by assessing repetition priming (that is, a reduction in signal change) at the stimulus (semantic), task (decision) and response levels. They showed that areas 44 and 8 (shown in orange) in caudal ventrolateral PFC showed repetition priming at the response level, that is, the signal change in these areas diminished when a motor response was repeated, regardless of the stimulus or decision associated with it. Area 45 (shown in blue) revealed repetition priming at the decision level even if the subsequent response differed. And area 47 (shown in red) demonstrated priming when the same item was encountered (semantic priming), regardless of the subsequent decision or response. These priming effects indicate a rostral-to-caudal gradient of decreasing abstraction. Part b is reproduced, with permission, from REF. 16 © (2007) MIT Press. Part c is reproduced, with permission, from REF. 113 © (2009) MIT press.