The capacity and motivation to be social is a key component of the human adaptive behavioral repertoire. Recent research has identified social behaviors remarkably similar to our own in other animals, including empathy, consolation, cooperation and strategic deception. Moreover, neurobiological studies in humans, nonhuman primates and rodents have identified shared brain structures—the so-called "social brain"— apparently specialized to mediate such functions. Neuromodulators may regulate social interactions by "tuning" the social brain, with important implications for treating social impairments. Here we survey recent findings in social neuroscience from a comparative perspective, and conclude that the very social behaviors that make us human emerge from mechanisms shared widely with other animals as well as some that appear to be unique to humans and other primates.

Sharika KM, Ramakrishnan A, Murthy A. Control of predictive error correction during a saccadic double-step task. J Neurophysiol 100: 2757-2770, 2008. First published September 24, 2008 doi:10.1152/jn.90238.2008. We explored the nature of control during error correction using a modified saccadic double-step task in which subjects cancelled the initial saccade to the first target and redirected gaze to a second target. Failure to inhibit was associated with a quick corrective saccade, suggesting that errors and corrections may be planned concurrently. However, because saccade programming constitutes a visual and a motor stage of preparation, the extent to which parallel processing occurs in anticipation of the error is not known. To estimate the time course of error correction, a triple-step condition was introduced that displaced the second target during the error. In these trials, corrective saccades directed at the location of the target prior to the third step suggest motor preparation of the corrective saccade in parallel with the error. To estimate the time course of motor preparation of the corrective saccade, further, we used an accumulator model (LATER) to fit the reaction times to the triple-step stimuli; the best-fit data revealed that the onset of correction could occur even before the start of the error. The estimated start of motor correction was also observed to be delayed as target step delay decreased, suggesting a form of interference between concurrent motor programs. Taken together we interpret these results to indicate that predictive error correction may occur concurrently while the oculomotor system is trying to inhibit an unwanted movement and suggest how inhibitory control and error correction may interact to enable goal-directed behaviors.

Our ability to regulate behavior based on past experience has thus far been examined using single movements. However, natural behavior typically involves a sequence of movements. Here, we examined the effect of previous trial type on the concurrent planning of sequential saccades using a unique paradigm. The task consisted of two trial types: no-shift trials, which implicitly encouraged the concurrent preparation of the second saccade in a subsequent trial; and target-shift trials, which implicitly discouraged the same in the next trial. Using the intersaccadic interval as an index of concurrent planning, we found evidence for contextbased preparation of sequential saccades. We also used functional MRI-guided, single-pulse, transcranial magnetic stimulation on human subjects to test the role of the supplementary eye field (SEF) in the proactive control of sequential eye movements. Results showed that (i) stimulating the SEF in the previous trial disrupted the previous trial type-based preparation of the second saccade in the nonstimulated current trial, (ii) stimulating the SEF in the current trial rectified the disruptive effect caused by stimulation in the previous trial, and (iii) stimulating the SEF facilitated the preparation of second saccades based on previous trial type even when the previous trial was not stimulated. Taken together, we show how the human SEF is causally involved in proactive preparation of sequential saccades.performance monitoring | delayed saccade double-step task | oculomotor | parallel programming | cognitive control T he medial frontal cortex has previously been implicated in our ability to regulate behavior based on past experience. For example, in the case of eye movements, the supplementary eye fields (SEFs) are involved in preparing a saccade in a given trial taking into account information related to preceding trials (1-3). Such contextual control is pivotal in generating optimal responses in a dynamically changing environment and may derive from signals that are sensitive to conflict or errors in previous trials (1-11). Although studies centered on proactive control have so far focused on the regulation of single movements or simple responses, natural behavior typically involves the execution of multiple movements in a sequence. Using a modified version of the classic double-step paradigm called the delayed saccade double-step task, we tested the role of previous trial type in modulating the concurrent planning of sequential eye movements (experiment 1). Also, using functional MRI (fMRI)-guided, single-pulse, transcranial magnetic stimulation (TMS), we investigated the role of SEF in the proactive planning of sequential saccades (experiment 2) i.e., whether the SEF is causally involved in embedding contextual information about the previous trial for the preparation of future sequential movements. In the process, we attempt to provide a link between apparently diverse functions of the SEF, such as planning of saccade sequences (12, 13) and conflict monitoring (1-3).The delayed...

The concurrent planning of sequential saccades offers a simple model to study the nature of visuomotor transformations since the second saccade vector needs to be remapped to foveate the second target following the first saccade. Remapping is thought to occur through egocentric mechanisms involving an efference copy of the first saccade that is available around the time of its onset. In contrast, an exocentric representation of the second target relative to the first target, if available, can be used to directly code the second saccade vector. While human volunteers performed a modified double-step task, we examined the role of exocentric encoding in concurrent saccade planning by shifting the first target location well before the efference copy could be used by the oculomotor system. The impact of the first target shift on concurrent processing was tested by examining the end-points of second saccades following a shift of the second target during the first saccade. The frequency of second saccades to the old versus new location of the second target, as well as the propagation of first saccade localization errors, both indices of concurrent processing, were found to be significantly reduced in trials with the first target shift compared to those without it. A similar decrease in concurrent processing was obtained when we shifted the first target but kept constant the second saccade vector. Overall, these results suggest that the brain can use relatively stable visual landmarks, independent of efference copy-based egocentric mechanisms, for concurrent planning of sequential saccades.

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