A genetically defined tecto-thalamic pathway drives a system of superior-colliculus-dependent visual cortices

Cortical responses to visual stimuli are believed to rely on the geniculo-striate pathway. However, recent work has challenged this notion by showing that responses in the postrhinal cortex (POR), a visual cortical area, instead depend on the tecto-thalamic pathway, which conveys visual information to the cortex via the superior colliculus (SC). Does POR's SC-dependence point to a wider system of tecto-thalamic cortical visual areas? What information might this system extract from the visual world? We discovered multiple mouse cortical areas whose visual responses rely on SC, with the most lateral showing the strongest SC-dependence. This system is driven by a genetically defined cell type that connects the SC to the pulvinar thalamic nucleus. Finally, we show that SC-dependent cortices distinguish self-generated from externally generated visual motion. Hence, lateral visual areas comprise a system that relies on the tecto-thalamic pathway and contributes to processing visual motion as animals move through the environment.

Possible rodent equivalent of the posterior cingulate cortex (area 23) interconnects with multimodal cortical and subcortical regions

Posterior cingulate cortex (area 23, A23) in human and monkeys is a critical component of the default mode network and is involved in many diseases such as Alzheimer's disease, autism, depression, attention deficit hyperactivity disorder and schizophrenia. However, A23 has not yet identified in rodents, and this makes modeling related circuits and diseases in rodents very difficult. Using a comparative approach, molecular markers and unique connectional patterns this study has uncovered the location and extent of possible rodent equivalent (A23~) of the primate A23. A23 ~ but not adjoining areas in the rodents displays strong reciprocal connections with anteromedial thalamic nucleus. Rodent A23 ~ reciprocally connects with the medial pulvinar and claustrum as well as with anterior cingulate, granular retrosplenial, medial orbitofrontal, postrhinal, and visual and auditory association cortices. Rodent A23 ~ projects to dorsal striatum, ventral lateral geniculate nucleus, zona incerta, pretectal nucleus, superior colliculus, periaqueductal gray, and brainstem. All these findings support the versatility of A23 in the integration and modulation of multimodal sensory information underlying spatial processing, episodic memory, self-reflection, attention, value assessment and many adaptive behaviors. Additionally, this study also suggests that the rodents could be used to model monkey and human A23 in future structural, functional, pathological, and neuromodulation studies.

Geometric determinants of the postrhinal egocentric spatial map

Animals use the geometry of their local environments to orient themselves during navigation. Single neurons in the rat postrhinal cortex (POR) appear to encode environmental geometry in an egocentric (self-centered) reference frame, such that they fire in response to the egocentric bearing and/or distance from the environment center or boundaries. One major issue is whether these neurons truly encode high-level global parameters, such as the bearing/distance of the environment centroid, or whether they are simply responsive to the bearings and distances of nearby walls. We recorded from POR neurons as rats foraged in environments with different geometric layouts and modeled their responses based on either global geometry (centroid) or local boundary encoding. POR neurons largely split into either centroid-encoding or local-boundary-encoding cells, with each group lying at one end of a continuum. We also found that distance-tuned cells tend to scale their linear tuning slopes in a very small environment, such that they lie somewhere between absolute and relative distance encoding. In addition, POR cells largely maintain their bearing preferences, but not their distance preferences, when exposed to different boundary types (opaque, transparent, drop edge), suggesting different driving forces behind the bearing and distance signals. Overall, the egocentric spatial correlates encoded by POR neurons comprise a largely robust and comprehensive representation of environmental geometry.

A model for transforming egocentric views into goal-directed behavior

Neurons in the rat postrhinal cortex (POR) respond to the egocentric (observer-centered) bearing and distance of the boundaries, or geometric center, of an enclosed space. Understanding of the precise geometric and sensory properties of the environment that generate these signals is limited. Here we model how this signal may relate to visual perception of motion parallax along environmental boundaries. A behavioral extension of this tuning is the known 'centering response', in which animals follow a spatial gradient function based on boundary parallax to guide behavior toward the center of a corridor or enclosure. Adding an allocentric head direction signal to this representation can translate the gradient across two-dimensional space and provide a new gradient for directing behavior to any location. We propose a model for how this signal may support goal-directed navigation via projections to the dorsomedial striatum. The result is a straightforward code for navigational variables derived from visual geometric properties of the surrounding environment, which may be used to map space and transform incoming sensory information into an appropriate motor output.

The Interaction of Cue Type and Its Associated Behavioral Response Dissociates the Neural Activity between the Perirhinal and Postrhinal Cortices

The perirhinal cortex (PER) and postrhinal cortex (POR) in the medial temporal lobe are commonly described as two distinct systems that process nonspatial and spatial information, respectively. Recent findings suggest that the two regions exhibit functional overlap when processing stimulus information, especially when associative responses are required in goal-directed behavior. However, we lack the neural correlates of this. In the current study, we recorded spiking activities for single units of the PER and POR as rats were required to choose a response associated with the identity of a visual object or scene stimulus. We found that similar proportions of cells fired selectively for either scene or object between the two regions. In the PER and POR, response-selective neurons showed higher contrast for different responses than stimulus-selective cells did for stimuli. More cells fired selectively for specific choice response in the POR than in the PER. The differential firing patterns of the PER and POR were best explained when the stimulus and response components were considered together: Stimulus-selective cells were modulated more by the response in the POR than in the PER, whereas response-selective cells in the PER were modulated more by object information than by scenes. Our results suggest that in a goal-directed memory task, the information processing in the PER and POR may be dynamically modulated not only by input stimulus information but also by the associated choice behavior and stimulus–response interaction.

Functional Differentiation of Dorsal and Ventral Posterior Parietal Cortex of the Rat: Implications for Controlled and Stimulus-Driven Attention

The posterior parietal cortex (PPC) is important for visuospatial attention. The primate PPC shows functional differentiation such that dorsal areas are implicated in top-down, controlled attention, and ventral areas are implicated in bottom-up, stimulus-driven attention. Whether the rat PPC also shows such functional differentiation is unknown. Here, we address this open question using functional neuroanatomy and in vivo electrophysiology. Using conventional tract-tracing methods, we examined connectivity with other structures implicated in visuospatial attention including the lateral posterior nucleus of the thalamus (LPn) and the postrhinal cortex (POR). We showed that the LPn projects to the entire PPC, preferentially targeting more ventral areas. All parts of the PPC and POR are reciprocally connected with the strongest connections evident between ventral PPC and caudal POR. Next, we simultaneously recorded neuronal activity in dorsal and ventral PPC as rats performed a visuospatial attention (VSA ) task that engages in both bottom-up and top-down attention. Previously, we provided evidence that the dorsal PPC is engaged in multiple cognitive process including controlled attention (Yang et al. 2017). Here, we further showed that ventral PPC cells respond to stimulus onset more rapidly than dorsal PPC cells, providing evidence for a role in stimulus-driven, bottom-up attention.

Modular Network between Postrhinal Visual Cortex, Amygdala, and Entorhinal Cortex

The postrhinal area (POR) is a known center for integrating spatial with nonspatial visual information and a possible hub for influencing landmark navigation by affective input from the amygdala. This may involve specific circuits within muscarinic acetylcholine receptor 2 (M2)-positive (M2+) or M2- modules of POR that associate inputs from the thalamus, cortex, and amygdala, and send outputs to the entorhinal cortex. Using anterograde and retrograde labeling with conventional and viral tracers in male and female mice, we found that all higher visual areas of the ventral cortical stream project to the amygdala, while such inputs are absent from primary visual cortex and dorsal stream areas. Unexpectedly for the presumed salt-and-pepper organization of mouse extrastriate cortex, tracing results show that inputs from the dorsal lateral geniculate nucleus and lateral posterior nucleus were spatially clustered in layer 1 (L1) and overlapped with M2+ patches of POR. In contrast, input from the amygdala to L1 of POR terminated in M2- interpatches. Importantly, the amygdalocortical input to M2- interpatches in L1 overlapped preferentially with spatially clustered apical dendrites of POR neurons projecting to amygdala and entorhinal area lateral, medial (ENTm). The results suggest that subnetworks in POR, used to build spatial maps for navigation, do not receive direct thalamocortical M2+ patch-targeting inputs. Instead, they involve local networks of M2- interpatches, which are influenced by affective information from the amygdala and project to ENTm, whose cells respond to visual landmark cues for navigation.SIGNIFICANCE STATEMENT A central purpose of visual object recognition is identifying the salience of objects and approaching or avoiding them. However, it is not currently known how the visual cortex integrates the multiple streams of information, including affective and navigational cues, which are required to accomplish this task. We find that in a higher visual area, the postrhinal cortex, the cortical sheet is divided into interdigitating modules receiving distinct inputs from visual and emotion-related sources. One of these modules is preferentially connected with the amygdala and provides outputs to entorhinal cortex, constituting a processing stream that may assign emotional salience to objects and landmarks for the guidance of goal-directed navigation.

Goal-directed interaction of stimulus and task demand in the parahippocampal region

The hippocampus and parahippocampal region are essential for representing episodic memories involving various spatial locations and objects, and for using those memories for future adaptive behavior. The “dual‐stream model” was initially formulated based on anatomical characteristics of the medial temporal lobe, dividing the parahippocampal region into two streams that separately process and relay spatial and nonspatial information to the hippocampus. Despite its significance, the dual‐stream model in its original form cannot explain recent experimental results, and many researchers have recognized the need for a modification of the model. Here, we argue that dividing the parahippocampal region into spatial and nonspatial streams a priori may be too simplistic, particularly in light of ambiguous situations in which a sensory cue alone (e.g., visual scene) may not allow such a definitive categorization. Upon reviewing evidence, including our own, that reveals the importance of goal‐directed behavioral responses in determining the relative involvement of the parahippocampal processing streams, we propose the Goal‐directed Interaction of Stimulus and Task‐demand (GIST) model. In the GIST model, input stimuli such as visual scenes and objects are first processed by both the postrhinal and perirhinal cortices—the postrhinal cortex more heavily involved with visual scenes and perirhinal cortex with objects—with relatively little dependence on behavioral task demand. However, once perceptual ambiguities are resolved and the scenes and objects are identified and recognized, the information is then processed through the medial or lateral entorhinal cortex, depending on whether it is used to fulfill navigational or non‐navigational goals, respectively. As complex sensory stimuli are utilized for both navigational and non‐navigational purposes in an intermixed fashion in naturalistic settings, the hippocampus may be required to then put together these experiences into a coherent map to allow flexible cognitive operations for adaptive behavior to occur.

Involvement of the Postrhinal and Perirhinal Cortices in Microscale and Macroscale Visuospatial Information Encoding

Whereas the postrhinal cortex (POR) is a critical center for the integration of egocentric and allocentric spatial information, the perirhinal cortex (PRC) plays an important role in the encoding of objects that supports spatial learning. The POR and PRC send afferents to the hippocampus, a structure that builds complex associative memories from the spatial experience. Hippocampal encoding of item-place experience is accompanied by the nuclear expression of immediate early gene (IEGs). Subfields of the Cornus ammonius and subregions of the hippocampus exhibit differentiated and distinct encoding responses, depending on whether the spatial location and relationships of large highly visible items (macroscale encoding) or small partially concealed items (microscale encoding), is learned. But to what extent the PRC and POR support hippocampal processing of different kinds of item-place representations is unclear. Using fluorescence in situ hybridization (FISH), we examined the effect of macroscale (overt, landmark) and microscale (subtle, discrete) item-place learning on the nuclear expression of the IEG, Arc. We observed an increase in Arc mRNA in the caudal part of PRC area 35 and the caudal part of the POR after macroscale, but not microscale item-place learning. The caudal part of PRC area 36, the rostral and middle parts of PRC areas 35 and 36, as well as the middle part of the POR responded to neither type of item. These results suggest that macroscale items may contain a strong identity component that is processed by specific compartments of the PRC and POR. In contrast small, microscale items are not encoded by the POR or PRC, indicating that item dimensions may play a role in the involvement of these structures in item processing.

A Conditioning-Strengthened Circuit From CA1 of Dorsal Hippocampus to Basolateral Amygdala Participates in Morphine-Withdrawal Memory Retrieval

Conditioned context-induced retrieval of drug withdrawal memory contributes to drug relapse. The basolateral amygdala (BLA) is an important brain region that is involved in conditioned context-induced retrieval of morphine withdrawal memory. However, the upstream pathways of the activation of the BLA by conditioned context remains to be studied. The present results show that the CA1 of dorsal hippocampus is an upstream brain region of the activation of the BLA during conditioned context-induced morphine withdrawal memory retrieval; the indirect connection from the CA1 of dorsal hippocampus to the BLA is enhanced in mice with conditioned place aversion (CPA); the postrhinal cortex (POR) is a brain region that connects the CA1 of dorsal hippocampus and the activation of the BLA during conditioned context-induced retrieval of morphine-withdrawal memory. These results suggest that a conditioning-strengthened indirect circuit from the CA1 of dorsal hippocampus to the BLA through the POR participates in morphine withdrawal memory retrieval.

Differential role of interleukin-1β in neuroinflammation-induced impairment of spatial and nonspatial memory in hyperammonemic rats

Activated microglia and increased brain IL-1β play a main role in cognitive impairment in much pathology. We studied the role of IL-1β in neuroinflammation-induced impairment of the following different types of learning and memory: novel object recognition (NOR), novel object location (NOL), spatial learning, reference memory (RM), and working memory (WM). All these processes are impaired in hyperammonemic rats. We assessed which of these types of learning and memory are restored by blocking the IL-1 receptor in vivo in hyperammonemic rats and the possible mechanisms involved. Blocking the IL-1 receptor reversed microglial activation in the hippocampus, perirhinal cortex, and prefrontal cortex but not in the postrhinal cortex. This was associated with the restoration of NOR and WM but not of tasks involving a spatial component (NOL and RM). This suggests that IL-1β would be involved in neuroinflammation-induced nonspatial memory impairment, whereas spatial memory impairment would be IL-1β-independent and would be mediated by other proinflammatory factors.-Taoro-González, L., Cabrera-Pastor, A., Sancho-Alonso, M., Arenas, Y. M., Meseguer-Estornell, F., Balzano, T., ElMlili, N., Felipo, V. Differential role of interleukin-1β in neuroinflammation-induced impairment of spatial and nonspatial memory in hyperammonemic rats.

An identified ensemble within a neocortical circuit encodes essential information for genetically-enhanced visual shape learning

Advanced cognitive tasks are encoded in distributed neocortical circuits that span multiple forebrain areas. Nonetheless, synaptic plasticity and neural network theories hypothesize that essential information for performing these tasks is encoded in specific ensembles within these circuits. Relatively simpler subcortical areas contain specific ensembles that encode learning, suggesting that neocortical circuits contain such ensembles. Previously, using localized gene transfer of a constitutively active protein kinase C (PKC), we established that a genetically-modified circuit in rat postrhinal cortex, part of the hippocampal formation, can encode some essential information for performing specific visual shape discriminations. However, these studies did not identify any specific neurons that encode learning; the entire circuit might be required. Here, we show that both learning and recall require fast neurotransmitter release from an identified ensemble within this circuit, the transduced neurons; we blocked fast release from these neurons by coexpressing a Synaptotagmin I siRNA with the constitutively active PKC. During learning or recall, specific signaling pathways required for learning are activated in this ensemble; during learning, calcium/calmodulin-dependent protein kinase II, MAP kinase, and CREB are activated; and, during recall, dendritic protein synthesis and CREB are activated. Using activity-dependent gene imaging, we showed that during learning, activity in this ensemble is required to recruit and activate the circuit. Further, after learning, during image presentation, blocking activity in this ensemble reduces accuracy, even though most of the rest of the circuit is activated. Thus, an identified ensemble within a neocortical circuit encodes essential information for performing an advanced cognitive task.

Shared Functions of Perirhinal and Parahippocampal Cortices: Implications for Cognitive Aging

A predominant view of perirhinal cortex (PRC) and postrhinal/parahippocampal cortex (POR/PHC) function contends that these structures are tuned to represent objects and spatial information, respectively. However, known anatomical connectivity, together with recent electrophysiological, neuroimaging, and lesion data, indicate that both brain areas participate in spatial and nonspatial processing. Instead of content-based organization, the PRC and PHC/POR may participate in two computationally distinct cortical-hippocampal networks: one network that is tuned to process coarse information quickly, forming gist-like representations of scenes/environments, and a second network tuned to process information about the specific sensory details that are necessary for discrimination across sensory modalities. The available data suggest that the latter network may be more vulnerable in advanced age.

Postnatal development of retrosplenial projections to the parahippocampal region of the rat

The rat parahippocampal region (PHR) and retrosplenial cortex (RSC) are cortical areas important for spatial cognition. In PHR, head-direction cells are present before eye-opening, earliest detected in postnatal day (P)11 animals. Border cells have been recorded around eye-opening (P16), while grid cells do not obtain adult-like features until the fourth postnatal week. In view of these developmental time-lines, we aimed to explore when afferents originating in RSC arrive in PHR. To this end, we injected rats aged P0-P28 with anterograde tracers into RSC. First, we characterized the organization of RSC-PHR projections in postnatal rats and compared these results with data obtained in the adult. Second, we described the morphological development of axonal plexus in PHR. We conclude that the first arriving RSC-axons in PHR, present from P1 onwards, already show a topographical organization similar to that seen in adults, although the labeled plexus does not obtain adult-like densities until P12.

DOI:http://dx.doi.org/10.7554/eLife.13925.001

Our ability to navigate critically depends on part of the brain called the parahippocampal region. Within this region, there are several different types of brain cells (or neurons) whose activity “codes” different aspects of navigation, such as position, direction and speed.

To understand how parahippocampal neurons are able to form these activity patterns, we need to understand how they develop connections with neurons from other brain regions that are important for navigation, such as the retrosplenial cortex. If inputs from retrosplenial neurons are important for generating the activity patterns observed in the parahippocampal region, the connections between the two groups of neurons should be fully mature before the activity patterns emerge. In rats, this should occur around 11–16 days after birth.

Sugar and Witter have now assessed how the retrosplenial inputs are organized in the parahippocampal region of rats. This revealed that, when the rats are born, there are very few retrosplenial inputs present in the parahippocampal region. However, the few inputs that are present are organized similarly to how they eventually will be organized in adults. After birth, the number of inputs gradually increases until the rats are approximately 12 days old, at which point the pattern of connections is indistinguishable from what we observe in adults. Thus it appears that retrosplenial inputs are fully mature before activity patterns emerge in the parahippocampal region.

In the future, Sugar and Witter would like to investigate how inputs to the parahippocampal region are able to organize themselves during early development. The importance of retrosplenial inputs could also be investigated by manipulating them during development and adulthood.

DOI:http://dx.doi.org/10.7554/eLife.13925.002

Insular projections to the parahippocampal region in the rat

The insular cortex is involved in the perception of interoceptive signals, coding of emotional and affective states, and processing information from gustatory, olfactory, auditory, somatosensory, and nociceptive modalities. This information represents an important component of episodic memory, mediated by the parahippocampal-hippocampal region. A comprehensive description of insular projections to the latter region is lacking. Previous studies reported that insular projections do not target any of the subdivisions in the hippocampal formation (the dentate gyus, the cornu ammonis [CA] fields 1, 2, and 3 and the subiculum), but, in contrast, target the parahippocampal region (perirhinal, postrhinal, lateral and medial entorhinal cortices, and pre- and parasubiculum). The present study examined the topographical and laminar organization of insular projections to the parahippocampal region in the rat with the use of anterograde tracing. Notably, our results corroborated the absence of hippocampal projections. We further showed that the perirhinal and the lateral entorhinal cortices received extensive projections from the insular cortex, primarily from its agranular areas. With the exception of a weak projection to the postrhinal cortex, projections to the remaining parahippocampal areas were either absent or very sparse. The projections to the lateral entorhinal cortex displayed a preference for the deep layers of its most lateral subdivisions, known also to receive hippocampal inputs. Projections to the perirhinal cortex primarily targeted the superficial layers with a preference for its ventral subdivision, referred to as area 35. Our findings indicate that only processed information, reflecting emotional and affective states, but not primary gustatory and viscerosensory information, has direct access to the parahippocampal-hippocampal system.

Topographic organization of orbitofrontal projections to the parahippocampal region in rats

The parahippocampal region, which comprises the perirhinal, postrhinal, and entorhinal cortices, as well as the pre- and parasubiculum, receives inputs from several association cortices and provides the major cortical input to the hippocampus. This study examined the topographic organization of projections from the orbitofrontal cortex (OFC) to the parahippocampal region in rats by injecting anterograde tracers, biotinylated dextran amine (BDA) and Phaseolus vulgaris-leucoagglutinin (PHA-L), into four subdivisions of OFC. The rostral portion of the perirhinal cortex receives strong projections from the medial (MO), ventral (VO), and ventrolateral (VLO) orbitofrontal areas and the caudal portion of lateral orbitofrontal area (LO). These projections terminate in the dorsal bank and fundus of the rhinal sulcus. In contrast, the postrhinal cortex receives a strong projection specifically from VO. All four subdivisions of OFC give rise to projections to the dorsolateral parts of the lateral entorhinal cortex (LEC), preferentially distributing to more caudal levels of LEC. The medial entorhinal cortex (MEC) receives moderate input from VO and weak projections from MO, VLO, and LO. The presubiculum receives strong projections from caudal VO but only weak projections from other OFC regions. As for the laminar distribution of projections, axons originating from OFC terminate more densely in upper layers (layers I-III) than in deep layers in the parahippocampal region. These results thus show a striking topographic organization of OFC-to-parahippocampal connectivity. Whereas LO, VLO, VO, and MO interact with perirhinal-LEC circuits, the interactions with postrhinal cortex, presubiculum, and MEC are mediated predominantly through the projections of VO.

Genetic enhancement of visual learning by activation of protein kinase C pathways in small groups of rat cortical neurons

Although learning and memory theories hypothesize that memories are encoded by specific circuits, it has proven difficult to localize learning within a cortical area. Neural network theories predict that activation of a small fraction of the neurons in a circuit can activate that circuit. Consequently, altering the physiology of a small group of neurons might potentiate a specific circuit and enhance learning, thereby localizing learning to that circuit. In this study, we activated protein kinase C (PKC) pathways in small groups of neurons in rat postrhinal (POR) cortex. We microinjected helper virus-free herpes simplex virus vectors that expressed a constitutively active PKC into POR cortex. This PKC was expressed predominantly in glutamatergic and GABAergic neurons in POR cortex. This intervention increased phosphorylation of five PKC substrates that play critical roles in neurotransmitter release (GAP-43 and dynamin) or glutamatergic neurotransmission (specific subunits of AMPA or NMDA receptors and myristoylated alanine-rich C kinase substrate). Additionally, activation of PKC pathways in cultured cortical neurons supported activation-dependent increases in release of glutamate and GABA. This intervention enhanced the learning rate and accuracy of visual object discriminations. In individual rats, the numbers of transfected neurons positively correlated with this learning. During learning, neuronal activity was increased in neurons proximal to the transfected neurons. These results demonstrate that potentiating small groups of glutamatergic and GABAergic neurons in POR cortex enhances visual object learning. More generally, these results suggest that learning can be mediated by specific cortical circuits.

Functionally dissociating aspects of event memory: the effects of combined perirhinal and postrhinal cortex lesions on object and place memory in the rat

Reciprocal interactions between the hippocampus and the perirhinal and parahippocampal cortices form core components of a proposed temporal lobe memory system. For this reason, the involvement of the hippocampus in event memory is thought to depend on its connections with these cortical areas. Contrary to these predictions, we found that NMDA-induced lesions of the putative rat homologs of these cortical areas (perirhinal plus postrhinal cortices) did not impair performance on two allocentric spatial tasks highly sensitive to hippocampal dysfunction. Remarkably, for one of the tasks there was evidence of a facilitation of performance. The same cortical lesions did, however, disrupt spontaneous object recognition and object discrimination reversal learning but spared initial acquisition of the discrimination. This pattern of results reveals important dissociations between different aspects of memory within the temporal lobe. Furthermore, it shows that the perirhinal-postrhinal cortex is not a necessary route for spatial information reaching the hippocampus and that object familiarity-novelty detection depends on different neural substrates than do other aspects of event memory.