Perceptual decision making requires a complex set of computations to implement, evaluate, and adjust the conversion of sensory input into a categorical judgment. Little is known about how the specific underlying computations are distributed across and within different brain regions. Using a reaction-time (RT) motion direction-discrimination task, we show that a unique combination of decision-related signals is represented in monkey frontal eye field (FEF). Some responses were modulated by choice, motion strength, and RT, consistent with a temporal accumulation of sensory evidence. These responses converged to a threshold level prior to behavioral responses, reflecting decision commitment. Other responses continued to be modulated by motion strength even after decision commitment, possibly providing a memory trace to help evaluate and adjust the decision process with respect to rewarding outcomes. Both response types were encoded by FEF neurons with both narrow- and broad-spike waveforms, presumably corresponding to inhibitory interneurons and excitatory pyramidal neurons, respectively, and with diverse visual, visuomotor, and motor properties, albeit with different frequencies. Thus, neurons throughout FEF appear to make multiple contributions to decision making that only partially overlap with contributions from other brain regions. These results help to constrain how networks of brain regions interact to generate perceptual decisions.
This paper puts some perspective in the usually communicated statement that LIP neurons are responsible for perceptual decision making in monkeys who perform a reaction time motion discrimination task. Especially, the authors report on neurons in frontal eye field (FEF) that also show typical accumulation-to-bound responses. Furthermore, at least as many neurons in FEF exhibited activity that was correlated with motion coherence and choice during and after the saccade indicating a choice and extinguishing the stimulus, i.e., the activity of these neurons appeared to accumulate evidence, but seemed to ignore the supposed bound and maintained a representation of the stimulus after it had gone. In the discussion the authors also point to other studies which found activity that can be interpreted in terms of evidence accumulation. Corresponding neurons have been found in LIP, FEF, superior colliculus (SC) and caudate nucleus of which neurons in LIP and SC may be mostly governed by a bound. From the reported and reviewed results it becomes clear that, although accumulation-to-bound may be an important component of perceptual decision making, it is not sufficient to explain the wide variety of decision-related neuronal activity in the brain. In particular, it is unclear how neurons from the mentioned brain regions interact and what their different roles in perceptual decision making are.