Spatial Relationship between Flavoprotein Fluorescence and the Hemodynamic Response in the Primary Visual Cortex of Alert Macaque Monkeys

Flavoprotein fluorescence imaging (FFI) is a novel intrinsic optical signal that is steadily gaining ground as a valuable imaging tool in neuroscience research due to its closer relationship with local metabolism relative to the more commonly used hemodynamic signals. We have developed a technique for FFI imaging in the primary visual cortex (V1) of alert monkeys. Due to the nature of neurovascular coupling, hemodynamic signals are known to spread beyond the locus of metabolic activity. To determine whether FFI signals could provide a more focal measure of cortical activity in alert animals, we compared FFI and hemodynamic point spreads (i.e. responses to a minimal visual stimulus) and functional mapping signals over V1 in macaques performing simple fixation tasks. FFI responses were biphasic, with an early and focal fluorescence increase followed by a delayed and spatially broader fluorescence decrease. As expected, the early fluorescence increase, indicating increased local oxidative metabolism, was somewhat narrower than the simultaneously observed hemodynamic response. However, the later FFI decrease was broader than the hemodynamic response and started prior to the cessation of visual stimulation suggesting different mechanisms underlying the two phases of the fluorescence signal. FFI mapping signals were free of vascular artifacts and comparable in amplitude to hemodynamic mapping signals. These results indicate that the FFI response may be a more local and direct indicator of cortical metabolism than the hemodynamic response in alert animals

Single Scale for Odor Intensity in Rat Olfaction

SummaryHumans and laboratory animals are thought to discriminate sensory objects using elemental perceptual features computed by neural circuits in the brain [1, 2]. However, it is often difficult to identify the perceptual features that animals use to make specific comparisons. In olfaction, changes in the concentration of a given odor lead to discriminable changes in both its perceived quality [3, 4] and intensity [5, 6]. Humans use perceived intensity to compare quantities of different odors. Here we establish that laboratory rats also use perceived intensity to compare concentrations of different odors and reveal the perceptual organization of this elemental feature. We first trained rats to classify concentrations of single odors as high or low. When subsequently classifying concentrations of two odors presented on different trials of the same session, rats made errors consistent with using a single intensity criterion for both odors. This allowed us to investigate the relative perceived intensity of different odor pairs. Odor intensity was not only a function of concentration, but varied also with molecular weight and exposure time. These findings demonstrate the role of perceived intensity as an elemental perceptual feature of odors in rat olfaction

Rapid triggering of vocalizations following social interactions

SummarySocial interactions are multifaceted, composed of interlinked sensory-motor behaviors. The individual significance of each of these correlated components cannot be established without observing the full behavior. Recently, Wesson [1] concluded that rats display their submissive status by lowering sniff rate following face-to-face encounters with a dominant conspecific. How rats can perceive such changes in sniff rate is unclear. We recorded sniffing and vocal production of rats during social interactions. Face-to-face encounters with a dominant rat immediately elicited 22 kHz alarm calls in the submissive. The large drop in sniff rate observed in submissive rats was caused by the prolonged exhalations needed to produce these calls. We propose that, while submissive rats do lower sniffing rates around face-to-face encounters, dominant rats need not directly perceive this change, but may instead attend to the salient 22 kHz alarm calls

Rodent ultrasonic vocalizations are bound to active sniffing behavior

During rodent active behavior, multiple orofacial sensorimotor behaviors, including sniffing and whisking, display rhythmicity in the theta range (~5-10 Hz). During specific behaviors, these rhythmic patterns interlock, such that execution of individual motor programs becomes dependent on the state of the others. Here we performed simultaneous recordings of the respiratory cycle and ultrasonic vocalization emission by adult rats and mice in social settings. We used automated analysis to examine the relationship between breathing patterns and vocalization over long time periods. Rat ultrasonic vocalizations (USVs, ’50 kHz’) were emitted within stretches of active sniffing (5−10 Hz) and were largely absent during periods of passive breathing (1-4 Hz). Because ultrasound was tightly linked to the exhalation phase, the sniffing cycle segmented vocal production into discrete calls and imposed its theta rhythmicity on their timing. In turn, calls briefly prolonged exhalations, causing an immediate drop in sniffing rate. Similar results were obtained in mice. Our results show that ultrasonic vocalizations are an integral part of the rhythmic orofacial behavioral ensemble. This complex behavioral program is thus involved not only in active sensing but also in the temporal structuring of social communication signals. Many other social signals of mammals, including monkey calls and human speech, show structure in the theta range. Our work points to a mechanism for such structuring in rodent ultrasonic vocalizations

Task-related hemodynamic responses are modulated by reward and task engagement.

Hemodynamic recordings from visual cortex contain powerful endogenous task-related responses that may reflect task-related arousal, or "task engagement" distinct from attention. We tested this hypothesis with hemodynamic measurements (intrinsic-signal optical imaging) from monkey primary visual cortex (V1) while the animals' engagement in a periodic fixation task over several hours was varied through reward size and as animals took breaks. With higher rewards, animals appeared more task-engaged; task-related responses were more temporally precise at the task period (approximately 10-20 seconds) and modestly stronger. The 2-5 minute blocks of high-reward trials led to ramp-like decreases in mean local blood volume; these reversed with ramp-like increases during low reward. The blood volume increased even more sharply when the animal shut his eyes and disengaged completely from the task (5-10 minutes). We propose a mechanism that controls vascular tone, likely along with local neural responses in a manner that reflects task engagement over the full range of timescales tested

Shifts in responses for each algorithm condition.

There is greater overlap of bands in the 95-algorithm condition compared to the 65-algorithm condition, demonstrating that the 95-algorithm influenced decisions to a greater degree than the 65-algorithm.</p