Complementary encoding of spatial information in hippocampal astrocytes.

Calcium dynamics into astrocytes influence the activity of nearby neuronal structures. However, because previous reports show that astrocytic calcium signals largely mirror neighboring neuronal activity, current information coding models neglect astrocytes. Using simultaneous two-photon calcium imaging of astrocytes and neurons in the hippocampus of mice navigating a virtual environment, we demonstrate that astrocytic calcium signals encode (i.e., statistically reflect) spatial information that could not be explained by visual cue information. Calcium events carrying spatial information occurred in topographically organized astrocytic subregions. Importantly, astrocytes encoded spatial information that was complementary and synergistic to that carried by neurons, improving spatial position decoding when astrocytic signals were considered alongside neuronal ones. These results suggest that the complementary place dependence of localized astrocytic calcium signals may regulate clusters of nearby synapses, enabling dynamic, context-dependent variations in population coding within brain circuits.

A model of head direction and landmark coding in complex environments.

Environmental information is required to stabilize estimates of head direction (HD) based on angular path integration. However, it is unclear how this happens in real-world (visually complex) environments. We present a computational model of how visual feedback can stabilize HD information in environments that contain multiple cues of varying stability and directional specificity. We show how combinations of feature-specific visual inputs can generate a stable unimodal landmark bearing signal, even in the presence of multiple cues and ambiguous directional specificity. This signal is associated with the retrosplenial HD signal (inherited from thalamic HD cells) and conveys feedback to the subcortical HD circuitry. The model predicts neurons with a unimodal encoding of the egocentric orientation of the array of landmarks, rather than any one particular landmark. The relationship between these abstract landmark bearing neurons and head direction cells is reminiscent of the relationship between place cells and grid cells. Their unimodal encoding is formed from visual inputs via a modified version of Oja's Subspace Algorithm. The rule allows the landmark bearing signal to disconnect from directionally unstable or ephemeral cues, incorporate newly added stable cues, support orientation across many different environments (high memory capacity), and is consistent with recent empirical findings on bidirectional HD firing reported in the retrosplenial cortex. Our account of visual feedback for HD stabilization provides a novel perspective on neural mechanisms of spatial navigation within richer sensory environments, and makes experimentally testable predictions.

Neurons including hippocampal spatial view cells, and navigation in primates including humans.

A new theory is proposed of mechanisms of navigation in primates including humans in which spatial view cells found in the primate hippocampus and parahippocampal gyrus are used to guide the individual from landmark to landmark. The navigation involves approach to each landmark in turn (taxis), using spatial view cells to identify the next landmark in the sequence, and does not require a topological map. Two other cell types found in primates, whole body motion cells, and head direction cells, can be utilized in the spatial view cell navigational mechanism, but are not essential. If the landmarks become obscured, then the spatial view representations can be updated by self-motion (idiothetic) path integration using spatial coordinate transform mechanisms in the primate dorsal visual system to transform from egocentric to allocentric spatial view coordinates. A continuous attractor network or time cells or working memory is used in this approach to navigation to encode and recall the spatial view sequences involved. I also propose how navigation can be performed using a further type of neuron found in primates, allocentric-bearing-to-a-landmark neurons, in which changes of direction are made when a landmark reaches a particular allocentric bearing. This is useful if a landmark cannot be approached. The theories are made explicit in models of navigation, which are then illustrated by computer simulations. These types of navigation are contrasted with triangulation, which requires a topological map. It is proposed that the first strategy utilizing spatial view cells is used frequently in humans, and is relatively simple because primates have spatial view neurons that respond allocentrically to locations in spatial scenes. An advantage of this approach to navigation is that hippocampal spatial view neurons are also useful for episodic memory, and for imagery.

Neuronal vector coding in spatial cognition.

Several types of neurons involved in spatial navigation and memory encode the distance and direction (that is, the vector) between an agent and items in its environment. Such vectorial information provides a powerful basis for spatial cognition by representing the geometric relationships between the self and the external world. Here, we review the explicit encoding of vectorial information by neurons in and around the hippocampal formation, far from the sensory periphery. The parahippocampal, retrosplenial and parietal cortices, as well as the hippocampal formation and striatum, provide a plethora of examples of vector coding at the single neuron level. We provide a functional taxonomy of cells with vectorial receptive fields as reported in experiments and proposed in theoretical work. The responses of these neurons may provide the fundamental neural basis for the (bottom-up) representation of environmental layout and (top-down) memory-guided generation of visuospatial imagery and navigational planning.

Mental rotation ability and spontaneous brain activity: a magnetoencephalography study.

We performed experiments using magnetoencephalography to clarify the relationship between three-dimensional visuospatial abilities and spontaneous visual thinking characteristics. Subjects were divided into two groups based on the rate of correct answers to mental rotation tasks: those with good performances (Group G) and those with bad performances (Group B). We found the followings: (1) in the mental rotation tasks, the 25-35 Hz lower γ band activities in the superior parietal lobule/intraparietal sulcus regions and in the occipitotemporal region were significantly larger in Group G than in Group B and (2) in the spontaneous mental imagery tasks, the 20-Hz band activity in the left premotor cortex and the 35-Hz band activity in the supplementary motor area were significantly larger in Group G.

Changes in brain activation related to visuo-spatial memory after real-time fMRI neurofeedback training in healthy elderly and Alzheimer's disease.

Cognitive decline is a symptom of healthy ageing and Alzheimer's disease. We examined the effect of real-time fMRI based neurofeedback training on visuo-spatial memory and its associated neuronal response. Twelve healthy subjects and nine patients of prodromal Alzheimer's disease were included. The examination spanned five days (T1-T5): T1 contained a neuropsychological pre-test, the encoding of an itinerary and a fMRI-based task related that itinerary. T2-T4 hosted the real-time fMRI neurofeedback training of the parahippocampal gyrus and on T5 a post-test session including encoding of another itinerary and a subsequent fMRI-based task were done. Scores from neuropsychological tests, brain activation and task performance during the fMRI-paradigm were compared between pre and post-test as well as between healthy controls and patients. Behavioural performance in the fMRI-task remained unchanged, while cognitive testing showed improvements in visuo-spatial memory performance. Both groups displayed task-relevant brain activation, which decreased in the right precentral gyrus and left occipital lobe from pre to post-test in controls, but increased in the right occipital lobe, middle frontal gyrus and left frontal lobe in the patient group. While results suggest that the training has affected brain activation differently between controls and patients, there are no pointers towards a behavioural manifestation of these changes. Future research is required on the effects that can be induced using real-time fMRI based neurofeedback training and the required training duration to elicit broad and lasting effects.

Analysis of Visuospatial Abilities in Chiari Malformation Type I.

The involvement of the cerebellum in visuospatial abilities has been evidenced in numerous studies, based on the cerebellar-cortical circuitry. This domain has been evaluated in several patients with cerebellar disorders, but the assessment of visuospatial processing in Chiari malformation type I (CM-I) is scarce. The aim of this study is to analyze the visuospatial performance between CM-I adult patients and healthy controls. Participants have been tested using Block Design and Visual Puzzles subtests of the Wechsler Adult Intelligence Scale (WAIS), the Benton Judgment of Line Orientation test, and the Rey-Osterrieth Complex Figure test. The anxious-depressive symptomatology, the physical pain, and the premorbid intelligence have been controlled for, as well. The CM-I patients showed a significantly lower performance; however, after analyzing and controlling for the effect of clinical variables and psychopathological symptomatology, the main effect was maintained for visual puzzles and line orientation tasks. The findings suggest that CM-I patients show a poorer performance in tasks that require an exercise of perceptual reasoning without motor demand, accompanied by visualization and mental imagery of the stimuli. This study contributes towards the reinforcement of the evidence on the cognitive alterations associated to CM-I.

Do questionnaires reflect their purported cognitive functions?

Questionnaires are used widely across psychology and permit valuable insights into a person's thoughts and beliefs, which are difficult to derive from task performance measures alone. Given their importance and widespread use, it is vital that questionnaires map onto the cognitive functions they purport to reflect. However, where performance on naturalistic tasks such as imagination, autobiographical memory, future thinking and navigation is concerned, there is a dearth of knowledge about the relationships between task performance and questionnaire measures. Questionnaires are also typically designed to probe a specific aspect of cognition, when instead researchers sometimes want to obtain a broad profile of a participant. To the best of our knowledge, no questionnaire exists that asks simple single questions about a wide range of cognitive functions. To address these gaps in the literature, we recruited a large sample of participants (n=217), all of whom completed a battery of widely used questionnaires and performed naturalistic tasks involving imagination, autobiographical memory, future thinking and navigation. We also devised a questionnaire that comprised simple single questions about the cognitive functions of interest. There were four main findings. First, imagination and navigation questionnaires reflected performance on their related tasks. Second, memory questionnaires were associated with autobiographical memory vividness and not internal (episodic) details. Third, imagery questionnaires were more associated with autobiographical memory vividness and future thinking than the questionnaires purporting to reflect these functions. Finally, initial exploratory analyses suggested that a broad profile of information can be obtained efficiently using a small number of simple single questions, and these modelled task performance comparably to established questionnaires in young, healthy adults. Overall, while some questionnaires can act as proxies for behaviour, the relationships between memory and future thinking tasks and questionnaires are more complex and require further elucidation.

Thalamocortical processing of the head-direction sense.

Our thoughts and sensations are examples of cognitive processes that emerge from the collective activity of billions of neurons in the brain. Thalamocortical circuits form the canonical building-blocks of the brain networks supporting the most complex cognitive functions. How these neurons communicate and interact has been the focus of extensive research in "classical" sensory systems. Similar to visual, auditory or somatosensory thalamic pathways, one primary nucleus in the anterior (limbic) thalamus - the antero-dorsal nucleus - conveys a low-level input, the head-direction (HD) signal, to the cortex. Its activity is controlled in large part by the vestibular system and is relayed by a serially connected group of subcortical nuclei to the thalamus. HD cells serve as the brain's internal 'compass' and each of them is tuned to the specific direction the animal is facing. Recently, recordings of HD neuronal populations in the antero-dorsal nucleus and its main cortical target, the post-subiculum, have revealed that neuronal activity in the thalamocortical HD network are largely invariant to brain states at three levels: static (preserved functional organization), temporal (same drifting speed during exploration and Rapid Eye Movement sleep) and inter-area interaction (from thalamus to cortex). These observations suggest that HD neurons are certainly more driven by intrinsic wiring and dynamics than by sensory inputs and that the information flows bottom-up, even during sleep. Altogether, thalamic HD cells convey a highly reliable, near-noiseless signal that broadly influences the emergence of spatial maps in the cortex and may play a key role in sleep-dependent memory processes.

Effectiveness of the method of loci is only minimally related to factors that should influence imagined navigation.

The method of loci is arguably the most famous mnemonic strategy and is highly effective for memorising lists of non-spatial information in order. As described and instructed, this strategy apparently relies on a spatial/navigational metaphor. The user imagines moving through an environment, placing (study) and reporting (recall) list items along the way. However, whether the method relies critically on this spatial/navigation metaphor is unknown. An alternative hypothesis is that the navigation component is superfluous to memory success, and the method of loci is better viewed as a special case of a larger class of imagery-based peg strategies. Training participants on three virtual environments varying in their characteristics (an apartment, an open field, and a radial-arm maze), we asked participants to use each trained environment as the basis of the method of loci to learn five 11-word lists. Performance varied significantly across environment. However, the effects were small in magnitude. Further tests suggested that navigation-relevant knowledge and ability were not major determinants of success in verbal memory, even for participants who were confirmed to have been compliant with the strategy. These findings echo neuroimaging findings that navigation-based cognition does occur during application of the method of loci, but imagined navigation is unlikely to be directly responsible for its effectiveness. Instead, the method of loci may be best viewed as a variant of peg methods.

Photobiomodulation rescues cognitive flexibility in early stressed subjects.

Neglectful parenting is one of the most prevalent forms of child mistreatment. This early life stress leads to long-term alterations in all the psychological domains, as well as brain alterations. Animal models have been developed to emulate and further study this early life stress, and one of most widely used models is maternal separation. In both human and animal models, cognitive flexibility has been found to be altered. In this study, we performed maternal separation (10 days, 4 h per day) in rats, and in adulthood, we tested their spatial navigation and cognitive flexibility. In addition, we delivered photobiomodulation treatment (Low-level light therapy: 1064 nm, 30 mW, 60 cycles) on the rats' brains, and we tested energy oxidative metabolism using cytochrome c oxidase histochemistry. Early life stress delivered in the form of maternal separation on the first 10 postnatal days leads to cognitive flexibility impairment and a general increase in energy metabolism in adulthood. Low-level light therapy seems to be useful for treating these unwanted outcomes, because it rescued cognitive flexibility and returned the oxidative energy metabolism to balanced scores, without harming controls' brains or behavior. Photobiomodulation is a promising tool in the treatment of chronic stress-related consequences because it rescued cognitive flexibility.

Identifying the cognitive processes underpinning hippocampal-dependent tasks.

Autobiographical memory, future thinking, and spatial navigation are critical cognitive functions that are thought to be related and are known to depend upon a brain structure called the hippocampus. Surprisingly, direct evidence for their interrelatedness is lacking, as is an understanding of why they might be related. There is debate about whether they are linked by an underlying memory-related process or, as has more recently been suggested, because they each require the endogenous construction of scene imagery. Here, using a large sample of participants and multiple cognitive tests with a wide spread of individual differences in performance, we found that these functions are indeed related. Mediation analyses further showed that scene construction, and not memory, mediated (explained) the relationships between the functions. These findings offer a fresh perspective on autobiographical memory, future thinking, navigation, and also on the hippocampus, where scene imagery appears to play an influential role. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Encoding of 3D head direction information in the human brain.

Head direction cells are critical for navigation because they convey information about which direction an animal is facing within an environment. To date, most studies on head direction encoding have been conducted on a horizontal two-dimensional (2D) plane, and little is known about how three-dimensional (3D) direction information is encoded in the brain despite humans and other animals living in a 3D world. Here, we investigated head direction encoding in the human brain while participants moved within a virtual 3D "spaceship" environment. Movement was not constrained to planes and instead participants could move along all three axes in volumetric space as if in zero gravity. Using functional magnetic resonance imaging (fMRI) multivoxel pattern similarity analysis, we found evidence that the thalamus, particularly the anterior portion, and the subiculum encoded the horizontal component of 3D head direction (azimuth). In contrast, the retrosplenial cortex was significantly more sensitive to the vertical direction (pitch) than to the azimuth. Our results also indicated that vertical direction information in the retrosplenial cortex was significantly correlated with behavioral performance during a direction judgment task. Our findings represent the first evidence showing that the "classic" head direction system that has been identified on a horizontal 2D plane also seems to encode vertical and horizontal heading in 3D space in the human brain.

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.

Visuospatial exploration and art therapy intervention in patients with Parkinson's disease: an exploratory therapeutic protocol.

Though abnormalities of visuospatial function occur in Parkinson's disease, the impact of such deficits on functional independence and psychological wellbeing has been historically under- recognized, and effective treatments for this impairment are unknown. These symptoms can be encountered at any stage of the disease, affecting many activities of daily living, and negatively influencing mood, self-efficacy, independence, and overall quality of life. Furthermore, visuospatial dysfunction has been recently linked to gait impairment and falls, symptoms that are known to be poor prognostic factors. Here, we aim to present an original modality of neurorehabilitation designed to address visuospatial dysfunction and related symptoms in Parkinson's disease, known as "Art Therapy". Art creation relies on sophisticated neurologic mechanisms including shape recognition, motion perception, sensory-motor integration, abstraction, and eye-hand coordination. Furthermore, art therapy may enable subjects with disability to understand their emotions and express them through artistic creation and creative thinking, thus promoting self-awareness, relaxation, confidence and self-efficacy. The potential impact of this intervention on visuospatial dysfunction will be assessed by means of combined clinical, behavioral, gait kinematic, neuroimaging and eye tracking analyses. Potential favorable outcomes may drive further trials validating this novel paradigm of neurorehabilitation.

Supramammillary Nucleus Modulates Spike-Time Coordination in the Prefrontal-Thalamo-Hippocampal Circuit during Navigation.

During navigation, hippocampal spatial maps are thought to interact with action-planning systems in other regions of cortex. We here report a key role for spike-time coordination in functional coupling of the medial prefrontal cortex (mPFC) to the hippocampus through the thalamic nucleus reuniens (NR). When rats perform a T-maze alternation task, spikes of neurons in mPFC and NR exhibit enhanced coordination to the CA1 theta rhythm before the choice point on the maze. A similar coordination to CA1 theta rhythm was observed in neurons of the supramammillary nucleus (SUM). Optogenetic silencing of SUM neurons reduced the temporal coordination in the mPFC-NR-CA1 circuit. Following SUM inactivation, trajectory representations were impaired in both NR and CA1, but not in mPFC, indicating a failure in transmission of action plans from mPFC to the hippocampus. The findings identify theta-frequency spike-time coordination as a mechanism for gating of information flow in the mPFC-NR-CA1 circuit.

Unsupervised Discovery of Demixed, Low-Dimensional Neural Dynamics across Multiple Timescales through Tensor Component Analysis.

Perceptions, thoughts, and actions unfold over millisecond timescales, while learned behaviors can require many days to mature. While recent experimental advances enable large-scale and long-term neural recordings with high temporal fidelity, it remains a formidable challenge to extract unbiased and interpretable descriptions of how rapid single-trial circuit dynamics change slowly over many trials to mediate learning. We demonstrate a simple tensor component analysis (TCA) can meet this challenge by extracting three interconnected, low-dimensional descriptions of neural data: neuron factors, reflecting cell assemblies; temporal factors, reflecting rapid circuit dynamics mediating perceptions, thoughts, and actions within each trial; and trial factors, describing both long-term learning and trial-to-trial changes in cognitive state. We demonstrate the broad applicability of TCA by revealing insights into diverse datasets derived from artificial neural networks, large-scale calcium imaging of rodent prefrontal cortex during maze navigation, and multielectrode recordings of macaque motor cortex during brain machine interface learning.

Action affordances and visuo-spatial complexity in motor imagery: An fMRI study.

Imagining a complex action requires not only motor-related processing but also visuo-spatial imagery. In the current study, we examined visuo-spatial complexity and action affordances in motor imagery (MI). Using functional magnetic resonance imaging, we investigated the neural activity in MI of reach-to-grasp movements of the right hand in five conditions. Thirty participants were scanned while imagining grasping an everyday object, grasping a geometrical shape, grasping next to an everyday object, grasping next to a geometrical shape, and grasping at nothing (no object involved). We found that MI of grasping next to an object recruited the visuo-spatial cognition network including posterior parietal and premotor regions more strongly than MI of grasping an object. This indicates that grasping next to an object requires additional processing resources rendering MI more complex. MI of a grasping movement involving a familiar everyday object compared to a geometrical shape yielded stronger activation in motor-related regions, including the bilateral supplementary motor area. This activation might be due to inhibitory processes preventing motor execution of motor scripts evoked by everyday objects (action affordances). Our results indicate that visuo-spatial cognition plays a significant role in MI.

Influence of non-contextual auditory stimuli on navigation in a virtual reality context involving executive functions among patients after stroke.

BACKGROUND: Topographical disorientation is frequent among patients after a stroke and can be well explored with virtual environments (VEs). VEs also allow for the addition of stimuli. A previous study did not find any effect of non-contextual auditory stimuli on navigational performance in the virtual action planning-supermarket (VAP-S) simulating a medium-sized 3D supermarket. However, the perceptual or cognitive load of the sounds used was not high. OBJECTIVE: We investigated how non-contextual auditory stimuli with high load affect navigational performance in the VAP-S for patients who have had a stroke and any correlation between this performance and dysexecutive disorders. METHODS: Four kinds of stimuli were considered: sounds from living beings, sounds from supermarket objects, beeping sounds and names of other products that were not available in the VAP-S. The condition without auditory stimuli was the control. The Groupe de réflexion pour l'évaluation des fonctions exécutives (GREFEX) battery was used to evaluate executive functions of patients. RESULTS: The study included 40 patients who have had a stroke (n=22 right-hemisphere and n=18 left-hemisphere stroke). Patients' navigational performance was decreased under the 4 conditions with non-contextual auditory stimuli (P<0.05), especially for those with dysexecutive disorders. For the 5 conditions, the lower the performance, the more GREFEX tests were failed. Patients felt significantly disadvantaged by the non-contextual sounds sounds from living beings, sounds from supermarket objects and names of other products as compared with beeping sounds (P<0.01). Patients' verbal recall of the collected objects was significantly lower under the condition with names of other products (P<0.001). Left and right brain-damaged patients did not differ in navigational performance in the VAP-S under the 5 auditory conditions. CONCLUSIONS: These non-contextual auditory stimuli could be used in neurorehabilitation paradigms to train patients with dysexecutive disorders to inhibit disruptive stimuli.

Does ventrolateral prefrontal cortex help in searching for the lost key? Evidence from an fNIRS study.

The Key Search Task (KST) is a neuropsychological test that requires strategies for searching a lost key in an imaginary field. This request may involve different cognitive processes as mental imagery and navigation planning. This study was aimed at investigating, by a twenty-channel functional near-infrared spectroscopy (fNIRS) system, the hemodynamic response (i.e., oxygenated-hemoglobin (O2Hb) and deoxygenated-hemoglobin (HHb) changes) of the prefrontal cortex in navigation planning. A right ventrolateral prefrontal cortex (rVLPFC) activation during the KST was hypothesized. Thirty-eight volunteers performed the KST and a Control Task (CT), the latter requiring the volunteers to mark the X letter. An activation (i.e., increase/decrease in O2Hb/HHb) of: 1) rVLPFC during the KST execution, and 2) bilateral dorsolateral prefrontal cortex (DLPFC) during the CT execution was found. The present study provides a contribution in localizing the rVLPFC as the critically active region, within the frontal lobes, that was found maximally activated during mental navigation in the mind's eye of healthy participants while performing the KST. Considering the contribution of rVLPFC in spatial navigation, its activation suggests that the KST could be adopted in the clinical routine for investigating navigation planning. Compared to other neuroimaging techniques, fNIRS (with its relatively low physical constraints) contributes to better clarifying the role of rVLPFC in some aspects of human navigation. Therefore, the combined use of the fNIRS and the KST could be considered as an innovative and valid tool to evaluate fundamental functions for everyday life, such as spatial navigation planning.