BMI studies, where the reader mechanisms required to control an actuator are well defined by the experimenter, also support the view that assembly member contribution is non-isotropic (Fetz 2007). Multiple laboratories have reported that the most informative subset of 10 to 20 task-related motor cortex neurons can predict as much as 60 to 80% accuracy of limb position or gripping force, and adding further information from the remaining several dozens of simultaneously recorded neurons from either the motor cortex or other areas improve the prediction only by a modest 10 to 15% (Fig. 5b; Carmena et al., 2003; Hochberg et al, 2006; Serruya et al., 2002; Taylor et al., 2002; Wessberg et al., 2000; cf., Nicolelis and Lebedev, 2009). A similar hyperbolic relationship between the number of CA3 neurons and the occurrence of CA1 ‘ripples’ (‘reader pattern’) has been described in the hippocampus (Csicsvari et al., 2000). The diminishing returns obtained from increasing the assembly size in achieving target control in BMI studies can be interpreted in two different ways. First, that coordinated activity by a few or perhaps dozens
