Spatial tuning of face part representations within face-selective areas revealed by high-field fMRI

Regions sensitive to specific object categories as well as organized spatial patterns sensitive to different features have been found across the whole ventral temporal cortex (VTC). However, it is unclear that within each object category region, how specific feature representations are organized to support object identification. Would object features, such as object parts, be represented in fine-scale spatial tuning within object category-specific regions? Here, we used high-field 7T fMRI to examine the spatial tuning to different face parts within each face-selective region. Our results show consistent spatial tuning of face parts across individuals that within right posterior fusiform face area (pFFA) and right occipital face area (OFA), the posterior portion of each region was biased to eyes, while the anterior portion was biased to mouth and chin stimuli. Our results demonstrate that within the occipital and fusiform face processing regions, there exist systematic spatial tuning to different face parts that support further computation combining them.

Topographically localised modulation of tectal cell spatial tuning by natural scenes

Visual neurons can have their tuning properties contextually modulated by the presence of visual stimuli in the area surrounding their receptive field, especially when that stimuli contains natural features. However, stimuli presented in specific egocentric locations may have greater behavioural relevance, raising the possibility that the extent of contextual modulation may vary with position in visual space. To explore this possibility we utilised the small size and optical transparency of the larval zebrafish to describe the form and spatial arrangement of contextually modulated cells throughout an entire tectal hemisphere. We found that the spatial tuning of tectal neurons to a prey-like stimulus sharpens when the stimulus is presented in the context of a naturalistic visual scene. These neurons are confined to a spatially restricted region of the tectum and have receptive fields centred within a region of visual space in which the presence of prey preferentially triggers hunting behaviour. Our results demonstrate that circuits that support behaviourally relevant modulation of tectal neurons are not uniformly distributed. These findings add to the growing body of evidence that the tectum shows regional adaptations for behaviour.

Dynamic Spatial Tuning Patterns of Shoulder Muscles with Volunteers in a Driving Posture

Computational human body models (HBMs) of drivers for pre-crash simulations need active shoulder muscle control, and volunteer data are lacking. The goal of this paper was to build shoulder muscle dynamic spatial tuning patterns, with a secondary focus to present shoulder kinematic evaluation data. 8M and 9F volunteers sat in a driver posture, with their torso restrained, and were exposed to upper arm dynamic perturbations in eight directions perpendicular to the humerus. A dropping 8-kg weight connected to the elbow through pulleys applied the loads; the exact timing and direction were unknown. Activity in 11 shoulder muscles was measured using surface electrodes, and upper arm kinematics were measured with three cameras. We found directionally specific muscle activity and presented dynamic spatial tuning patterns for each muscle separated by sex. The preferred directions, i.e. the vector mean of a spatial tuning pattern, were similar between males and females, with the largest difference of 31° in the pectoralis major muscle. Males and females had similar elbow displacements. The maxima of elbow displacements in the loading plane for males was 189 ± 36 mm during flexion loading, and for females, it was 196 ± 36 mm during adduction loading. The data presented here can be used to design shoulder muscle controllers for HBMs and evaluate the performance of shoulder models.

Experience-dependent changes in hippocampal spatial activity and hippocampal circuit function are disrupted in a rat model of Fragile X Syndrome

Fragile X syndrome (FXS) is a common single gene cause of intellectual disability and Autism Spectrum Disorder. Cognitive inflexibility is one of the hallmarks of FXS, with affected individuals showing extreme difficulty adapting to novel or complex situations. To explore the neural correlates of this cognitive inflexibility, we used a rat model of FXS (Fmr1 KO), and recorded from the CA1 region of the hippocampus while animals habituated in a novel environment for two consecutive days. On the first day of exploration, the firing rate and spatial tuning of CA1 pyramidal neurons was similar between wild-type (WT) and Fmr1 KO rats. However, while CA1 pyramidal neurons from WT rats showed experience-dependent changes in firing and spatial tuning between the first and second day of exposure to the environment, these changes were decreased or absent in CA1 neurons of Fmr1 KO rats. These findings were consistent with increased excitability of Fmr1 KO CA1 neurons in ex-vivo hippocampal slices, which correlated with reduced synaptic inputs from the medial entorhinal cortex. Lastly, activity patterns of CA1 pyramidal neurons were discoordinated with respect to hippocampal oscillatory activity in Fmr1 KO rats. These findings suggest a network-level origin of cognitive deficits in FXS.

Topographically organized representation of space and context in the medial prefrontal cortex

Spatial tuning of pyramidal cells has been observed in diverse neocortical regions, but a systematic characterization of the properties of spatially tuned neurons across cortical layers and regions is lacking. Using mice navigating through virtual environments, we find topographical organizational principles for the representation of spatial features in the medial prefrontal cortex. We show that spatial tuning emerges across layers with a dorso-ventral gradient in the depth of spatial tuning, which resides in superficial layers. Moreover, the prefrontal cortex shows hemispheric lateralization of spatial tuning such that neurons located in the left hemisphere display more pronounced spatial tuning. During exploration of a novel compared to a familiar context, a different picture emerges. Context discrimination and familiarity detection is higher in superficial compared to deep layers. However, neurons of the right medial prefrontal cortex discriminate more efficiently between contexts than cells in the left hemisphere. Jointly, these results reveal a complex topographic organization of spatial representation and suggest a division of labor among prefrontal layers and subregions in the encoding of spatial position in the current environment and context discrimination.

Perceptual learning of pitch provided by cochlear implant stimulation rate

Cochlear implant users hear pitch evoked by stimulation rate, but discrimination diminishes for rates above 300 Hz. This upper limit on rate pitch is surprising given the remarkable and specialized ability of the auditory nerve to respond synchronously to stimulation rates at least as high as 3 kHz and arguably as high as 10 kHz. Sensitivity to stimulation rate as a pitch cue varies widely across cochlear implant users and can be improved with training. The present study examines individual differences and perceptual learning of stimulation rate as a cue for pitch ranking. Adult cochlear implant users participated in electrode psychophysics that involved testing once per week for three weeks. Stimulation pulse rate discrimination was measured in bipolar and monopolar configurations for apical and basal electrodes. Base stimulation rates between 100 and 800 Hz were examined. Individual differences were quantified using psychophysically derived metrics of spatial tuning and temporal integration. This study examined distribution of measures across subjects, predictive power of psychophysically derived metrics of spatial tuning and temporal integration, and the effect of training on rate discrimination thresholds. Psychophysical metrics of spatial tuning and temporal integration were not predictive of stimulation rate discrimination, but discrimination thresholds improved at lower frequencies with training. Since most clinical devices do not use variable stimulation rates, it is unknown to what extent recipients may learn to use stimulation rate cues if provided in a clear and consistent manner.

Conjunctive spatial and idiothetic codes are topographically organized in the lateral septum

The relevance of the hippocampal spatial code for downstream neuronal populations – in particular its main subcortical output, the lateral septum (LS) - is still poorly understood. Here, we addressed this knowledge gap by first clarifying the organization of LS afferents and efferents via retrograde and anterograde trans-synaptic tracing. We found that mouse LS receives inputs from hippocampal subregions CA1, CA3, and subiculum, and in turn projects directly to the lateral hypothalamus (LH), ventral tegmental area (VTA), and medial septum (MS). Next, we functionally characterized the spatial tuning properties of LS GABAergic cells, the principal cells composing the LS, via calcium imaging combined with unbiased analytical methods. We identified a significant number of cells that are modulated by place (38.01%), speed (23.71%), acceleration (27.84%), and head-direction (23.09%), and conjunctions of these properties, with spatial tuning comparable to hippocampal CA1 and CA3 place cells. Bayesian decoding of position on the basis of LS place cells accurately reflected the location of the animal. The distributions of cells exhibiting these properties formed gradients along the anterior-posterior axis of the LS, directly reflecting the organization of hippocampal inputs to the LS. A portion of LS place cells showed stable fields over the course of multiple days, potentially reflecting long-term episodic memory. Together, our findings demonstrate that the LS accurately and robustly represents spatial and idiothetic information and is uniquely positioned to relay this information from the hippocampus to the VTA, LH, and MS, thus occupying a key position within this distributed spatial memory network.