An Evasive Case of Gonococcal Endocarditis.

Neisseria gonorrhoeae is one of the most common sexually transmitted infections in the United States, and disseminated infection can lead to a variety of complications. This includes the less common, but potentially life-threatening complication of gonococcal endocarditis. The authors report a case of a formerly incarcerated middle-aged man with a three-day history of dyspnea on exertion, fever, headache, and productive cough with green sputum. He endorsed a several-week history of an untreated right molar infection but denied any history of genitourinary symptoms. Given concerns for heart failure, a transthoracic echocardiogram was obtained showing mitral regurgitation with a mass on the mitral valve leaflet, as well as a smaller aortic valve mass that was subsequently confirmed with a transesophageal echocardiogram. Initially, the patient was transferred from an outside hospital (OSH), and discrepancies were noted between the blood cultures obtained at the OSH and a private lab. Given that the patient was already started on antibiotics prior to transfer, a Karius assay was sent and returned positive for N. gonorrhoeae. He was started on empiric antibiotic coverage before ultimately undergoing mitral valve replacement with a mosaic valve. The patient completed six weeks of intravenous ceftriaxone with complete resolution of symptoms. This case demonstrates a rare incident of N. gonorrhoeae bacteremia without any common symptoms causing endocarditis and valvular destruction. Timely diagnosis, a multidisciplinary approach, and treatment of gonococcal endocarditis led to positive outcomes in this case.

Remembered reward locations restructure entorhinal spatial maps.

Ethologically relevant navigational strategies often incorporate remembered reward locations. Although neurons in the medial entorhinal cortex provide a maplike representation of the external spatial world, whether this map integrates information regarding learned reward locations remains unknown. We compared entorhinal coding in rats during a free-foraging task and a spatial memory task. Entorhinal spatial maps restructured to incorporate a learned reward location, which in turn improved positional decoding near this location. This finding indicates that different navigational strategies drive the emergence of discrete entorhinal maps of space and points to a role for entorhinal codes in a diverse range of navigational behaviors.

A Comparison of Neural Decoding Methods and Population Coding Across Thalamo-Cortical Head Direction Cells.

Head direction (HD) cells, which fire action potentials whenever an animal points its head in a particular direction, are thought to subserve the animal's sense of spatial orientation. HD cells are found prominently in several thalamo-cortical regions including anterior thalamic nuclei, postsubiculum, medial entorhinal cortex, parasubiculum, and the parietal cortex. While a number of methods in neural decoding have been developed to assess the dynamics of spatial signals within thalamo-cortical regions, studies conducting a quantitative comparison of machine learning and statistical model-based decoding methods on HD cell activity are currently lacking. Here, we compare statistical model-based and machine learning approaches by assessing decoding accuracy and evaluate variables that contribute to population coding across thalamo-cortical HD cells.

The Head-Direction Signal Plays a Functional Role as a Neural Compass during Navigation.

The rat limbic system contains head direction (HD) cells that fire according to heading in the horizontal plane, and these cells are thought to provide animals with an internal compass. Previous work has found that HD cell tuning correlates with behavior on navigational tasks, but a direct, causal link between HD cells and navigation has not been demonstrated. Here, we show that pathway-specific optogenetic inhibition of the nucleus prepositus caused HD cells to become directionally unstable under dark conditions without affecting the animals' locomotion. Then, using the same technique, we found that this decoupling of the HD signal in the absence of visual cues caused the animals to make directional homing errors and that the magnitude and direction of these errors were in a range that corresponded to the degree of instability observed in the HD signal. These results provide evidence that the HD signal plays a causal role as a neural compass in navigation.

Oscillatory synchrony between head direction cells recorded bilaterally in the anterodorsal thalamic nuclei.

The head direction (HD) circuit is a complex interconnected network of brain regions ranging from the brain stem to the cortex. Recent work found that HD cells corecorded ipsilaterally in the anterodorsal nucleus (ADN) of the thalamus displayed coordinated firing patterns. A high-frequency oscillation pattern (130-160 Hz) was visible in the cross-correlograms of these HD cell pairs. Spectral analysis further found that the power of this oscillation was greatest at 0 ms and decreased at greater lags, and demonstrated that there was greater synchrony between HD cells with similar preferred firing directions. Here, we demonstrate that the same high-frequency synchrony exists in HD cell pairs recorded contralaterally from one another in the bilateral ADN. When we examined the cross-correlograms of HD cells that were corecorded bilaterally, we observed the same high-frequency (~150- to 200-Hz) oscillatory relationship. The strength of this synchrony was similar to the synchrony seen in ipsilateral HD cell pairs, and the degree of synchrony in each cross-correlogram was dependent on the difference in tuning between the two cells. Additionally, the frequency rate of this oscillation appeared to be independent of the firing rates of the two cross-correlated cells. Taken together, these results imply that the left and right thalamic HD network are functionally related despite an absence of direct anatomical projections. However, anatomical tracing has found that each of the lateral mammillary nuclei (LMN) project bilaterally to both of the ADN, suggesting the LMN may be responsible for the functional connectivity observed between the two ADN.NEW & NOTEWORTHY This study used bilateral recording electrodes to examine whether head direction cells recorded simultaneously in both the left and right thalamus show coordinated firing. Cross-correlations of the cells' spike trains revealed a high-frequency oscillatory pattern similar to that seen in cross-correlations between pairs of ipsilateral head direction cells, demonstrating that the bilateral thalamic head direction signals may be part of a single unified network.

The nucleus prepositus hypoglossi contributes to head direction cell stability in rats.

Head direction (HD) cells in the rat limbic system fire according to the animal's orientation independently of the animal's environmental location or behavior. These HD cells receive strong inputs from the vestibular system, among other areas, as evidenced by disruption of their directional firing after lesions or inactivation of vestibular inputs. Two brainstem nuclei, the supragenual nucleus (SGN) and nucleus prepositus hypoglossi (NPH), are known to project to the HD network and are thought to be possible relays of vestibular information. Previous work has shown that lesioning the SGN leads to a loss of spatial tuning in downstream HD cells, but the NPH has historically been defined as an oculomotor nuclei and therefore its role in contributing to the HD signal is less clear. Here, we investigated this role by recording HD cells in the anterior thalamus after either neurotoxic or electrolytic lesions of the NPH. There was a total loss of direction-specific firing in anterodorsal thalamus cells in animals with complete NPH lesions. However, many cells were identified that fired in bursts unrelated to the animals' directional heading and were similar to cells seen in previous studies that damaged vestibular-associated areas. Some animals with significant but incomplete lesions of the NPH had HD cells that were stable under normal conditions, but were unstable under conditions designed to minimize the use of external cues. These results support the hypothesis that the NPH, beyond its traditional oculomotor function, plays a critical role in conveying vestibular-related information to the HD circuit.

The head-direction signal is critical for navigation requiring a cognitive map but not for learning a spatial habit.

Head-direction (HD) cells fire as a function of an animal's directional heading in the horizontal plane during two-dimensional navigational tasks [1]. The information from HD cells is used with place and grid cells to form a spatial representation (cognitive map) of the environment [2, 3]. Previous studies have shown that when rats are inverted (upside down), they have difficulty learning a task that requires them to find an escape hole from one of four entry points but that they can learn it when released from one or two start points [4]. Previous reports also indicate that the HD signal is disrupted when a rat is oriented upside down [5, 6]. Here we monitored HD cell activity in the two-entry-point version of the inverted task and when the rats were released from a novel start point. We found that despite the absence of direction-specific firing in HD cells when inverted, rats could successfully navigate to the escape hole when released from one of two familiar locations by using a habit-associated directional strategy. In the continued absence of normal HD cell activity, inverted rats failed to find the escape hole when started from a novel release point. The results suggest that the HD signal is critical for accurate navigation in situations that require a flexible allocentric cognitive mapping strategy, but not for situations that utilize habit-like associative spatial learning.