Article

Saccade target selection in the superior colliculus: A signal detection theory approach

Department of Physiology, University of Wisconsin-Madison, School of Medicine and Public Health, Madison, Wisconsin 53706, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.75). 04/2008; 28(12):2991-3007. DOI: 10.1523/JNEUROSCI.5424-07.2008
Source: PubMed

ABSTRACT How the brain selects one action from among multiple options is unknown. A main tenet of signal detection theory (SDT) is that sensory stimuli are represented as noisy information channels. Therefore, the accuracy of selection might be predicted by how well neuronal activity representing alternatives can be distinguished. Here, we apply an SDT framework to a motor system by recording from superior colliculus (SC) neurons during performance of a color, oddball selection task. We recorded from sets of four neurons simultaneously, each of the four representing one of the four possible targets. Because the electrode placement constrained the position of the stimuli in the visual field, the stimulus arrangement varied across experiments. This variability in stimulus arrangement led to variability in choices allowing us to explore the relationship between SC neuronal activity and performance accuracy. SC target neurons had higher levels of discharge than SC distractor neurons in subsets of trials when selection performance was very accurate. In subsets of trials when performance was poor, the discharge level decreased in target neurons and increased in distractor neurons. Accurate performance was associated with larger separations between neuronal activity from targets and distractors as quantified by the receiver operating characteristic (ROC) area and d' (an index of discriminability). Poorer performance was associated with less separation of target and distractor neuronal activity. ROC area and d' scaled approximately linearly with performance accuracy. Furthermore, ROC area and d' increased as saccade onset approached. Together, the results indicate that SC buildup neuronal activity signals the saccadic eye movement decision.

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    • "All of the results described above were based entirely on modulation of discharge rates of individual neurons. It is clear, though, that saccade target selection is accomplished by pools of neurons [148] [174] [175] and probably entails more than just modulation of spike rate because cooperation and competition between pairs of neurons is modulated during target selection [176]. Indeed, correlation in discharge rates of FEF neurons over longer time scales has been reported even before stimulus presentation [177]. "
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    • "In fact, several recent studies in primates have proposed that SC activity reflects decision-related variables, suggesting that it is directly involved in saccadic decisions (Horwitz et al. 2004; Kim and Basso 2008; Lee and Keller 2006). However, an outstanding question is whether the SC is involved only in motor decisions based on a modality that it explicitly represents—visual , auditory, or somatosensory— or whether it contributes to a wider class of decisions. "
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    • "Therefore, the activity difference between the two hemispheres of SC might restrict the reaction toward peripheral targets. This assumption is supported by a recent study suggesting that the activity difference among different populations of SC neurons reflects the certainty of direction choice in primates [85]. "
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