Network Dynamics Underlying Speed-Accuracy Trade-Offs in Response to Errors

The ability to dynamically and rapidly adjust task performance based on its outcome is fundamental to adaptive, flexible behavior. Over trials of a task, responses speed up until an error is committed and after the error responses slow down. These dynamic adjustments serve to optimize performance and are well-described by the speed-accuracy trade-off (SATO) function. We hypothesized that SATOs based on outcomes reflect reciprocal changes in the allocation of attention between the internal milieu and the task-at-hand, as indexed by reciprocal changes in activity between the default and dorsal attention brain networks. We tested this hypothesis using functional MRI to examine the pattern of network activation over a series of trials surrounding and including an error. We further hypothesized that these reciprocal changes in network activity are coordinated by the posterior cingulate cortex (PCC) and would rely on the structural integrity of its white matter connections. Using diffusion tensor imaging, we examined whether fractional anisotropy of the posterior cingulum bundle correlated with the magnitude of reciprocal changes in network activation around errors. As expected, reaction time (RT) in trials surrounding errors was consistent with predictions from the SATO function. Activation in the default network was: (i) inversely correlated with RT, (ii) greater on trials before than after an error and (iii) maximal at the error. In contrast, activation in the right intraparietal sulcus of the dorsal attention network was (i) positively correlated with RT and showed the opposite pattern: (ii) less activation before than after an error and (iii) the least activation on the error. Greater integrity of the posterior cingulum bundle was associated with greater reciprocity in network activation around errors. These findings suggest that dynamic changes in attention to the internal versus external milieu in response to errors underlie SATOs in RT and are mediated by the PCC

Abnormally persistent fMRI activation during antisaccades in schizophrenia: a neural correlate of perseveration

Objective: Impaired antisaccade performance is a consistent cognitive finding in schizophrenia. Antisaccades require both response inhibition and volitional motor programming, functions that are essential to flexible responding. We investigated whether abnormal timing of hemodynamic responses (HDRs) to antisaccades might contribute to perseveration of ocular motor responses in schizophrenia. We focused on the frontal eye field (FEF), which has been implicated in the persistent effects of antisaccades on subsequent responses in healthy individuals. Method: Eighteen chronic, medicated schizophrenia outpatients and 15 healthy controls performed antisaccades and prosaccades during functional MRI. Finite impulse response models provided unbiased estimates of event-related HDRs. We compared groups on the peak amplitude, time-to-peak, and full-width half-max of the HDRs. Results: In patients, HDRs in bilateral FEF were delayed and prolonged but ultimately of similar amplitude to that of controls. These abnormalities were present for antisaccades, but not prosaccades, and were not seen in a control region. More prolonged HDRs predicted slower responses in trials that followed an antisaccade. This suggests that persistent FEF activity following an antisaccade contributes to inter-trial effects on latency. Conclusions: Delayed and prolonged HDRs for antisaccades in schizophrenia suggest that the functions necessary for successful antisaccade performance take longer to implement and are more persistent. If abnormally persistent neural responses on cognitively demanding tasks are a more general feature of schizophrenia, they may contribute to response perseveration, a classic behavioral abnormality. These findings also underscore the importance of evaluating the temporal dynamics of neural activity to understand cognitive dysfunction in schizophrenia

Saccadic preparation in the frontal eye field is modulated by distinct trial history effects as revealed by magnetoencephalography. Cereb. Cortex 21, 245–253. doi: 10.1093/cercor/bhq057 Frontiers in Integrative Neuroscience www.frontiersin.org June 2014 |

Optimizing outcomes involves rapidly and continuously adjusting behavior based on context. While most behavioral studies focus on immediate task conditions, responses to events are also influenced by recent history. We used magnetoencephalography and a saccadic paradigm to investigate the neural bases of 2 trial history effects that are well characterized in the behavioral eye movement literature: task-switching and the prior-antisaccade effect. We found that switched trials were associated with increased errors and transient increases in activity in the frontal eye field (FEF) and anterior cingulate cortex early in the preparatory period. These activity changes are consistent with active reconfiguration of the task set, a time-limited process that is triggered by the instructional cue. Following an antisaccade versus prosaccade, there was increased activity in the FEF and prefrontal cortex that persisted into the preparatory period of the subsequent trial, and saccadic latencies were prolonged. We attribute these effects to persistent inhibition of the ocular motor response system from the prior antisaccade. These findings refine our understanding of how trial history interacts with current task demands to adjust responses. Such dynamic modulations of neural activity and behavior by recent experience are at the heart of adaptive flexible behavior

Speed-accuracy trade-offs during the antisaccade task.

<p>A: A schematic depiction of the speed-accuracy trade-off (SATO). As reaction time (RT) increases, the probability of an error decreases. The circle denotes the point where optimal accuracy is achieved with the fastest RT. Beyond this point, making faster responses entails a cost in reduced accuracy. B: The antisaccade paradigm. Schematic and timeline of the three conditions: easy, hard, and fake-hard. Each trial lasted four seconds and began with an instructional cue (300 ms), either a blue or yellow ‘X’ that indicated whether the trial was hard or easy. The mapping of cue color to trial type was counterbalanced across participants. The cue was horizontally flanked by two white squares of 0.4° width that marked the potential locations of stimulus appearance, 10° left and right of center. The squares remained visible for the duration of each run. At 300 ms, the instructional cue was replaced by a white fixation ring of 1.3° diameter at the center of the screen. At 1800 ms, the fixation ring disappeared (200 ms gap). At 2000 ms, the fixation ring reappeared at one of the two stimulus locations, right or left with equal probability. This was the imperative stimulus to which the participant responded by making a saccade in the opposite direction. The ring remained in the peripheral location for 1000 ms and then returned to the center, where participants were instructed to return their gaze for 1000 ms before the start of the next trial. Hard trials were distinguished by a 3 db increase in luminance of the peripheral squares starting during the gap. Except for the hard cue, fake-hard trials were identical to easy trials. Fixation epochs were simply a continuation of the fixation display that constitutes the final second of the previous saccadic trial. C: Mean saccadic RT as a function of trial position in relation to an error (ERR) with standard error bars.</p

fMRI activation and its relation to RT and to our theoretical prediction weightings.

<p>Maxima and locations of significant clusters within the default network and dorsal attention network. Clusterwise probabilities (CWP) are based on Monte Carlo correction for multiple comparisons within the default network and dorsal attention network ROIs. Local maxima (indented) are listed for clusters spanning both hemispheres.</p