SUMMARY Changes in pupil diameter that reflect effort and other cognitive factors are often interpreted in terms of the activity of norepinephrine-containing neurons in the brainstem nucleus locus coeruleus (LC), but there is little direct evidence for such a relationship. Here we show that LC activation reliably anticipates changes in pupil diameter that either fluctuate naturally or are driven by external events during near fixation, as in many psychophysical tasks. This relationship occurs on as fine a temporal and spatial scale as single spikes from single units. However, this relationship is not specific to the LC. Similar relationships, albeit with delayed timing and different reliabilities across sites, are evident in the inferior and superior colliculus and anterior and posterior cingulate cortex. Because these regions are interconnected with the LC, the results suggest that non-luminance-mediated changes in pupil diameter might reflect LC-mediated coordination of neuronal activity throughout some parts of the brain.

Neurons in the brainstem nucleus locus ceruleus (LC) often exhibit phasic activation in the context of simple sensory-motor tasks. The functional role of this activation, which leads to the release of norepinephrine throughout the brain, is not yet understood in part because the conditions under which it occurs remain in question. Early studies focused on the relationship of LC phasic activation to salient sensory events, whereas more recent work has emphasized its timing relative to goal-directed behavioral responses, possibly representing the end of a sensory-motor decision process. To better understand the relationship between LC phasic activation and sensory, motor, and decision processing, we recorded spiking activity of neurons in the LCϩ (LC and the adjacent, norepinephrine-containing subceruleus nucleus) of monkeys performing a countermanding task. The task required the monkeys to occasionally withhold planned, saccadic eye movements to a visual target. We found that many well isolated LCϩ units responded to both the onset of the visual cue instructing the monkey to initiate the saccade and again after saccade onset, even when it was initiated erroneously in the presence of a stop signal. Many of these neurons did not respond to saccades made outside of the task context. In contrast, neither the appearance of the stop signal nor the successful withholding of the saccade elicited an LCϩ response. Therefore, LCϩ phasic activation encodes sensory and motor events related to decisions to execute, but not withhold, movements, implying a functional role in goal-directed actions, but not necessarily more covert forms of processing.

Magnetic resonance imaging (MRI) is often used by electrophysiologists to target specific brain regions for placement of microelectrodes. However, the effectiveness of this technique has been limited by few methods to quantify in three dimensions the relative locations of brain structures, recording chambers and microelectrode trajectories. Here we present such a method. After surgical implantation, recording chambers are fitted with a plastic cylinder that is filled with a high-contrast agent to aid in the segmentation of the cylinder from brain matter in an MRI volume. The resulting images of the filled cylinder correspond to a virtual cylinder that is projected along its long axisparallel to the trajectories of microelectrodes advanced through the recording chamber -through the three-dimensional image of the brain. This technique, which does not require a stereotaxic coordinate system, can be used to quantify the coverage of an implanted recording chamber relative to anatomical landmarks at any depth or orientation. We have used this technique in conjunction with Caret (Van Essen et al., 2001) and AFNI (Cox, 1996) brain mapping software to successfully localize several regions of macaque cortex, including the middle temporal area, the lateral intraparietal area and the frontal eye field, and one subcortical structure, the locus coeruleus, for electrophysiological recordings.

Background: Ultrasound (U/S) guided peripheral IV catheter (PIV) placement is often needed after unsuccessful traditional IV attempts. Commercial U/S PIV training phantoms are expensive and difficult to alter. Non-commercial phantoms have been described; however, there has been no comparison of these models. The primary objectives of this study were to compare the echogenic and haptic properties of various non-commercial phantoms. Secondary objectives were to characterize the cost and ease of making the phantoms. Methods: This prospective observational study trialed six unique phantom models: Amini Ballistics; Morrow Ballistics; University of California San Diego (UCSD) gelatin; Rippey Chicken; Nolting Spam; and Johnson Tofu. Total cost and creation time were noted. Emergency Ultrasound Fellowship trained physicians performed U/S guided PIV placement on each model to evaluate their resemblance to human tissue haptic and echogenicity properties, utility for training, and comparability to commercial phantoms (Likert scale 1–5; higher performance = 5). Results: The Rippey model scored highest for each primary objective with an aggregate score of 4.8/5. UCSD ranked second and Nolting last for all primary objectives, with aggregate scores 3.7/5 and 1.3/5 respectively. Cost of production ranged from $4.39 (Johnson) to $29.76 (UCSD). Creation times ranged from 10 min (Johnson) to 120 min (UCSD). Conclusion: In our study the Rippey model performed best and offered a mid-level cost and creation time. Non-commercial U/S phantoms may represent cost-effective and useful PIV practice tools. Future studies should investigate the utility of these phantoms in teaching U/S guided PIV to novices and compare non-commercial to commercial phantoms.

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