Inactivation of face-selective neurons alters eye movements when free viewing faces

During free viewing, faces attract gaze and induce specific fixation patterns corresponding to the facial features. This suggests that neurons encoding the facial features are in the causal chain that steers the eyes. However, there is no physiological evidence to support a mechanistic link between face-encoding neurons in high-level visual areas and the oculomotor system. In this study, we targeted the middle face patches of the inferior temporal (IT) cortex in two macaque monkeys using an functional magnetic resonance imaging (fMRI) localizer. We then utilized muscimol microinjection to unilaterally suppress IT neural activity inside and outside the face patches and recorded eye movements while the animals free viewing natural scenes. Inactivation of the face-selective neurons altered the pattern of eye movements on faces: The monkeys found faces in the scene but neglected the eye contralateral to the inactivation hemisphere. These findings reveal the causal contribution of the high-level visual cortex in eye movements.

Hypometria of saccadic eye movements to targets in rapid circular motion

Saccades to objects moving on a straight trajectory take the velocity of the object into account. However, it is not known whether saccades can compensate for curved trajectories, nor is it known how they are affected by high target speeds. In Experiment 1, participants made a saccade in a delayed saccade task to a target moving in a circular trajectory. Surprisingly, saccades to high-speed moving targets were severely hypometric, with gains of only ∼55% for trajectories of the largest angular speed (2 revolutions per second) and eccentricity (12°). They also had unusually low peak velocities. In Experiment 2, the target jumped along a circular path around a central fixation point. Hypometria was still severe, except for very large jumps. Experiment 3 was like Experiment 1, except that a landmark was positioned on the trajectory of the target, and participants were instructed to make a saccade to the landmark or to its memorized location. This ameliorated hypometria considerably. Given the delayed nature of the tasks of Experiments 1 and 2, participants had considerable time to program a voluntary saccade to a location on the trajectory, if not to the rapidly moving target itself. Nevertheless, the abnormal saccade properties indicate that motor programming was compromised. These results indicate that motor output can be inextricably bound to sensory input to its detriment, even during a highly voluntary motor act; that apparent motion can produce this behavior; and that such abnormal saccades can be "rescued" by the presence of a stable visual goal.

Inactivation of face selective neurons alters eye movements when free viewing faces

During free viewing, faces attract gaze and induce specific fixation patterns corresponding to the facial features. This suggests that neurons encoding the facial features are in the causal chain that steers the eyes. However, there is no physiological evidence to support a mechanistic link between face encoding neurons in high-level visual areas and the oculomotor system. In this study, we targeted the middle face patches of inferior temporal (IT) cortex in two macaque monkeys using an fMRI localizer. We then utilized muscimol microinjection to unilaterally suppress IT neural activity inside and outside the face patches and recorded eye movements while the animals free viewing natural scenes. Inactivation of the face selective neurons altered the pattern of eye movements on faces: the monkeys found faces in the scene but neglected the eye contralateral to the inactivation hemisphere. These findings reveal the causal contribution of the high-level visual cortex in eye movements.

Significance

It has been shown, for more than half a century, that eye movements follow distinctive patterns when free viewing faces. This suggests causal involvement of the face-encoding visual neurons in the eye movements. However, the literature is scant of evidence for this possibility and has focused mostly on the link between low-level image saliency and eye movements. Here, for the first time, we bring causal evidence showing how face-selective neurons in inferior temporal cortex inform and steer eye movements when free viewing faces.

Surgical Procedure for Implantation of Opto-Array in Nonhuman Primates

Optogenetics allows precise temporal control of neuronal activity in the brain. Engineered viral vectors are routinely used to transduce neurons with light-sensitive opsins. However, reliable virus injection and light delivery in animals with large brains, such as nonhuman primates, has proven challenging. The Opto-Array is a novel yet simple device that is used to deliver light to extended regions of the cortex surface for high-throughput behavioral optogenetics in large brains. Here we present protocols for surgical delivery of virus (Basic Protocol 1) and implantation of the Opto-Array (Basic Protocol 2) in two separate surgeries in a rhesus monkey's inferior temporal cortex. As a proof of concept, we measured the behavioral performance of an animal detecting cortical optogenetic stimulations (Basic Protocol 3) with different illumination power and duration using the Opto-Array. The animal was able to detect the optogenetic stimulation for all tested illumination powers and durations. Regression analysis also showed both power and duration of illumination significantly modulate the detectability of the optogenetic stimulation. The outcome of this approach is superior to the standard practice of injecting and recording through a chamber for large areas of the cortex surface. Moreover, the chronic nature of the Opto-Array allows perturbation of neuronal activity of the same site across multiple sessions because it is highly stable; thus, data can be pooled over months. The detailed surgical method presented here makes it possible to use optogenetics to modulate neuronal activity across large regions of the cortex surface in the nonhuman primate brain. This method also lays the groundwork for future attempts to use optogenetics to restore vision in humans. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Virus injection surgery Basic Protocol 2: Opto-Array implantation surgery Basic Protocol 3: Cortical Perturbation Detection (CPD) task behavioral training.

Image-dependence of the detectability of optogenetic stimulation in macaque inferotemporal cortex

Artificial activation of neurons in early visual areas induces perception of simple visual flashes.1,2 Accordingly, stimulation in high-level visual cortices is expected to induce perception of complex features.3,4 However, results from studies in human patients challenge this expectation. Stimulation rarely induces any detectable visual event, and never a complex one, in human subjects with closed eyes.2 Stimulation of the face-selective cortex in a human patient led to remarkable hallucinations only while the subject was looking at faces.5 In contrast, stimulations of color- and face-selective sites evoke notable hallucinations independent of the object being viewed.6 These anecdotal observations suggest that stimulation of high-level visual cortex can evoke perception of complex visual features, but these effects depend on the availability and content of visual input. In this study, we introduce a novel psychophysical task to systematically investigate characteristics of the perceptual events evoked by optogenetic stimulation of macaque inferior temporal (IT) cortex. We trained macaque monkeys to detect and report optogenetic impulses delivered to their IT cortices7,8,9 while holding fixation on object images. In a series of experiments, we show that detection of cortical stimulation is highly dependent on the choice of images presented to the eyes and it is most difficult when fixating on a blank screen. These findings suggest that optogenetic stimulation of high-level visual cortex results in easily detectable distortions of the concurrent contents of vision.

Behavioral detectability of optogenetic stimulation of inferior temporal cortex varies with the size of concurrently viewed objects

We have previously demonstrated that macaque monkeys can behaviorally detect a subtle optogenetic impulse delivered to their inferior temporal (IT) cortex. We have also shown that the ability to detect the cortical stimulation impulse varies depending on some characteristics of the visual images viewed at the time of brain stimulation, revealing the visual nature of the perceptual events induced by stimulation of the IT cortex. Here we systematically studied the effect of the size of viewed objects on behavioral detectability of optogenetic stimulation of the central IT cortex. Surprisingly, we found that behavioral detection of the same optogenetic impulse highly varies with the size of the viewed object images. Reduction of the object size in four steps from 8 to 1 degree of visual angle significantly decreased detection performance. These results show that identical stimulation impulses delivered to the same neural population induce variable perceptual events depending on the mere size of the objects viewed at the time of brain stimulation.

Contextual saccade adaptation induced by sequential saccades

Saccade adaptation is the gradual adjustment of saccade end point to maintain spatial accuracy. Contextual adaptation refers to a situation in which the adaptation-related change in saccade end point is contingent on the behavioral context in which the saccade is made. For example, in some situations, the same saccade to the same retinotopic location can be simultaneously adapted in opposite directions depending on the context in which it is made. Saccade adaptation has traditionally been studied in isolated movements, but in everyday life, saccades are often planned and executed in sequences. The oculomotor system may therefore have adaptive mechanisms specific to sequential saccades. Here, in five experiments, we investigated contextual saccade adaptation in sequences of saccades. In the first experiment, we demonstrate that saccades to a given retinotopic location can be simultaneously adapted in opposite directions depending on whether they occur in isolation or in a sequence. In the other experiments, we measured the extent to which properties of the previous and following saccades in a sequence can induce contextual saccade adaptation. Overall, we find that the existence, direction, and amplitude of previous and subsequent saccades, as well as the order of the current saccade within a movement sequence, can all induce contextual adaptation. These novel findings demonstrate the surprising flexibility of the system in maintaining end point accuracy, and support the idea that saccades made in a movement sequence are planned concurrently rather than independently.NEW & NOTEWORTHY This study reveals a new type of contextual saccade adaptation: sequential saccades are able to induce contextual saccade adaptation when direction, amplitude, or the existence of preceding and following saccades are used as contexts. These novel findings are also consistent with the idea that saccades made in a sequence are planned concurrently rather than independently.

Toward next-generation primate neuroscience: A collaboration-based strategic plan for integrative neuroimaging

Open science initiatives are creating opportunities to increase research coordination and impact in nonhuman primate (NHP) imaging. The PRIMatE Data and Resource Exchange community recently developed a collaboration-based strategic plan to advance NHP imaging as an integrative approach for multiscale neuroscience.

Chronically implantable LED arrays for behavioral optogenetics in primates

Optogenetic methods have been widely used in rodent brains, but remain relatively under-developed for nonhuman primates such as rhesus macaques, an animal model with a large brain expressing sophisticated sensory, motor and cognitive behaviors. To address challenges in behavioral optogenetics in large brains, we developed Opto-Array, a chronically implantable array of light-emitting diodes for high-throughput optogenetic perturbation. We demonstrated that optogenetic silencing in the macaque primary visual cortex with the help of the Opto-Array results in reliable retinotopic visual deficits in a luminance discrimination task. We separately confirmed that Opto-Array illumination results in local neural silencing, and that behavioral effects are not due to tissue heating. These results demonstrate the effectiveness of the Opto-Array for behavioral optogenetic applications in large brains.

Modulation of saccade trajectories during sequential saccades

The planning and execution of sequential saccades can overlap in time, and abrupt changes in neural activity in the oculomotor system can alter the normal trajectory of saccades. In this study, we analyzed saccade trajectories to assess the combined programming of sequential saccades. In two separate psychophysical experiments, subjects were instructed to make a sequence of two saccades. The results showed modulation of saccade curvature by the direction and amplitude of both the preceding and following saccade: saccade curvature is modulated in the direction of preceding saccades and away from the direction of following saccades. Moreover, larger preceding and following saccades have stronger effects on curvature. These results support the idea that sequential saccades are programmed concurrently. Finally, the amount of saccade curvature is correlated with the deviation of saccade start and end points, and the time of maximum deviation of saccade trajectories is highly consistent in both experiments. Based on this, we propose a novel benefit for the modulation of saccade trajectories by the oculomotor system: minimizing the saccadic error in sequential saccades.NEW & NOTEWORTHY We show that in saccade sequences, saccade trajectory is modulated in the direction of the preceding saccade and away from the following saccade. The magnitude of this effect is correlated with preceding and following saccade amplitude. This confirms that programming of sequential saccades overlaps. Curvature is also correlated with the deviation of saccade start and end points. Thus, we propose a novel benefit for the modulation of saccade trajectories: minimizing end point error in sequential saccades.

Study of the in vitro and in vivo antileishmanial activities of nimodipine in susceptible BALB/c mice

BACKGROUND & OBJECTIVES

Pentavalent antimonials are the standard treatment for cutaneous leishmaniasis (CL), however, treatment failures are frequent. Nimodipine, a calcium channel blocker is known to show promising antiprotozoal effects. Here, we investigated the antileishmanial effect of Nimodipine in both in vitro and in vivo BALB/c mice model of CL. We also compared the in vivo effect with amphotericin B and meglumine antimoniate in the experimental CL mice model.

METHODS

Colorimetric alamar blue assay and J774 A.1 mouse macrophage cells were used to determine the effect of nimodipine on promastigotes and amastigotes viability, respectively. Then, the in vivo activity of nimodipine was compared to that of conventional therapies in both the early and established courses of Leishmania major infection in susceptible non-healing BALB/c mice.

RESULTS

Nimodipine was highly active against promastigotes and amastigotes of L. major with IC₅₀ values of 49.40 and 15.03 μM, respectively. In the early model, the combination therapy with meglumine antimoniate and nimodipine showed no parasites in the spleen or footpad of animals. The footpad thickness was significantly lower in mice treated with either nimodipine (1 mg/kg or 2.5 mg/kg) or amphotericin B compared to the control group in the established lesions model. However, no complete remission was observed in the footpad lesion of any of the treatment groups (nimodipine, amphotericin B, meglumine antimoniate, and combination therapy).

INTERPRETATION & CONCLUSION

The effect of nimodipine was comparable to that of amphotericin B and meglumine antimoniate in early and established CL lesion models. Since nimodipine is more cost-effective than conventional therapies, our results merit further investigation in other animal models and voluntary human subjects.

Visual cues that are effective for contextual saccade adaptation

The accuracy of saccades, as maintained by saccade adaptation, has been shown to be context dependent: able to have different amplitude movements to the same retinal displacement dependent on motor contexts such as orbital starting location. There is conflicting evidence as to whether purely visual cues also effect contextual saccade adaptation and, if so, what function this might serve. We tested what visual cues might evoke contextual adaptation. Over 5 experiments, 78 naive subjects made saccades to circularly moving targets, which stepped outward or inward during the saccade depending on target movement direction, speed, or color and shape. To test if the movement or context postsaccade were critical, we stopped the postsaccade target motion (experiment 4) or neutralized the contexts by equating postsaccade target speed to an intermediate value (experiment 5). We found contextual adaptation in all conditions except those defined by color and shape. We conclude that some, but not all, visual cues before the saccade are sufficient for contextual adaptation. We conjecture that this visual contextuality functions to allow for different motor states for different coordinated movement patterns, such as coordinated saccade and pursuit motor planning.

Hemolytic uremic syndrome caused by Shiga toxin-producing Escherichia coli 0111

Shiga toxin-producing Escherichia coli (STEC) was first discovered in 1977 and since has caused serious complications including the life-threatening condition of hemolytic uremic syndrome (HUS). While HUS is most common in children, adults and especially elderly patients experience a higher incidence of death and disability. Because the majority of HUS cases have been described in children, pediatric treatment options have been used to treat adult and elderly patients with HUS. More research regarding the treatment, risk factors, and prognosis of HUS in adults needs to be performed to ensure that optimal care is provided. The authors present a case series of 5 adults with HUS who were part of the largest outbreak of E coli 0111 reported in the United States. To date, there are no published cases of HUS secondary to E coli 0111 in adults. The authors also include a literature review of HUS secondary to STEC.