Kristian Lensjø

• Essner, Rachel A.; Ruda, Kiersten; Choh, Hannah J.; Kucukdereli, Hakan; Amsalem, Oren & Edelhaus, Julia [Show all 11 contributors for this article] (2026). Brainstem sensing of multiple body signals during food consumption. Neuron. ISSN 0896-6273. doi: 10.1016/j.neuron.2026.08.015. Full text in Research Archive
• Nymoen, Ingeborg; Rogge, Frederik Sebastian; Aasen, Anna Hjertvik; Grødem, Sverre; Malthe-Sørenssen, Anders & Lepperød, Mikkel Elle [Show all 9 contributors for this article] (2026). Task and Behavior-Related Variables Are Encoded by the Postrhinal and Medial Entorhinal Cortex During Non-Spatial Associative Learning. eLIFE. 14. doi: 10.7554/elife.106095.1. Full text in Research Archive Show summary

  The medial entorhinal cortex (MEC) is pivotal in spatial computations and episodic memory. In particular, an animal’s position can be decoded from the activity of entorhinal grid cells. However, it remains elusive whether MEC could play a more general role in different types of associative learning and how the representations develop during the learning process. It has been shown that the postrhinal cortex (POR), which is directly connected to MEC, integrates visual stimuli with salient outcomes. Here, we use a non-spatial visual association task to investigate whether MEC neurons represent low-level visual cues during learning. Using a Go/NoGo visual association task, we recorded neural activity in MEC and POR throughout the learning phase as mice associated drifting gratings with rewarded, aversive, or neutral outcomes. Our findings reveal that the neural tuning curves in both the POR and MEC change with the learning of the task. From the start of training, the POR neurons exhibited response tuning to the visual cues, and the tuning was stable to cue orientations during learning. In contrast, MEC neurons did not initially respond very strongly to visual cues but developed a robust tuning toward the rewarded trials. While the MEC’s representation of visual information was limited, it encoded other task elements. A large fraction of the neurons formed distinct functional clusters that were either activated or suppressed by reward-related behavior. Remarkably, these clusters segregated anatomically in MEC and maintained strong within-cluster correlations before and after training. Notably, although the same functional clusters were apparent in the POR, they did not show any anatomical structure as in the MEC. Task reversal induced significant changes in network responses across both regions, with a decrease in overall task-responsive neurons but a slight increase in stimulus representation. Strikingly, information about the choice to lick emerged with learning in both brain areas, and most significantly within the functional cell clusters representing reward consumption and plus-cue stimulus. Our results demonstrate that although neurons in MEC and POR develop behavior-modulated tuning during learning of a non-spatial visual association task, the MEC exhibits stronger within-cluster correlations and anatomical organization. Conversely, the POR population exhibits less structural organization and more specific stimulus-tuning, which is reflective of being a higher visual association area. Our findings reveal that the MEC can encode task– and behavior-related variables beyond spatial information.

• Grødem, Sverre; Thompson, Elise Holter; Røe, Malin Benum; Vatne, Guro Helén; Nymoen, Ingeborg & Buccino, Alessio Paolo [Show all 10 contributors for this article] (2025). Differential impacts of germline and adult aggrecan knockout in PV+ neurons on perineuronal nets and PV+ neuronal function. Molecular Psychiatry. ISSN 1359-4184. 30, p. 2907–2921. doi: 10.1038/s41380-025-02894-5. Full text in Research Archive Show summary

  Perineuronal nets (PNNs) are a condensed form of extracellular matrix primarily found around parvalbumin-expressing (PV+) interneurons. The postnatal maturation of PV+ neurons is accompanied with the formation of PNNs and reduced plasticity. Alterations in PNN and PV+ neuron function have been described for mental disorders such as schizophrenia and autism. The formation of PNNs is highly dependent on aggrecan, a proteoglycan encoded by the ACAN gene, but it remains unknown if it is produced by the PV+ neurons themselves. Thus, we established a knockout (KO) mouse model (ACANflx/PVcre) and an adeno-associated virus to specifically eliminate aggrecan production from PV+ neurons, in the germline or adult animals, respectively. The germline KO (ACANflx/PVcre) eliminated the expression of PNNs labeled by Wisteria floribunda agglutinin (WFA), the most commonly used PNN marker. Surprisingly, electrophysiological properties of PV+ interneurons and ocular dominance plasticity of adult ACANflx/PVcre mice were similar to controls. In contrast, AAV-mediated ACAN knockout in adult mice increased ocular dominance plasticity. Moreover, in vivo Chondroitinase ABC treatment of KO mice resulted in reduced firing rate of PV+ cells and increased frequency of spontaneous excitatory postsynaptic currents (sEPSC), a phenotype associated with chABC treatment of WT animals. These findings suggest that compensatory mechanisms may be activated during development in response to the germline loss of aggrecan. Indeed, qPCR of bulk tissue indicates that other PNN components, including neurocan and tenascin-R, are expressed at higher levels in the KO animals. Finally, behavioral testing revealed that ACANflx/PVcre mice had similar long-term memory as controls in the Morris water maze. However, they employed bolder search strategies during spatial learning and showed lower level of anxiety-related behavior in an open field and zero maze.

• Lensjø, Kristian; Nymoen, Ingeborg; Rogge, Frederik Sebastian; Tøndel, Kristin; Sugden, Arthur & Shurnayte, Inga [Show all 11 contributors for this article] (2025). Local inhibitory circuits mediate cortical reactivations and memory consolidation. Science Advances. 11(22), p. 1–14. doi: 10.1126/sciadv.adu9800. Full text in Research Archive Show summary

  Highly salient events activate neurons across various brain regions. During subsequent rest or sleep, the activity patterns of these neurons often correlate with those observed during the preceding experience. Growing evidence suggests that these reactivations play a crucial role in memory consolidation, the process by which experiences are solidified in cortical networks for long-term storage. Here, we use longitudinal two-photon Ca2+ imaging alongside paired LFP recordings in the hippocampus and cortex, to show that targeted manipulation of PV+ inhibitory neurons in the lateral visual cortex after daily training selectively attenuates cue-specific reactivations and learning, with only minute effects on spontaneous activity and no apparent effect on normal function such as visual cue–elicited responses during training. In control mice, reactivations were biased toward salient cues, persisted for hours after training had ended, and the prevalence of reactivations was aligned with the learning process. Overall, our results underscore a crucial role for cortical reactivations in memory consolidation.

• Grødem, Sverre; Nymoen, Ingeborg; Vatne, Guro Helén; Rogge, Frederik Sebastian; Björnsdottir, Valgerdur & Lensjø, Kristian [Show all 7 contributors for this article] (2023). An updated suite of viral vectors for in vivo calcium imaging using intracerebral and retro-orbital injections in male mice. Nature Communications. 14(1), p. 608–1. doi: 10.1038/s41467-023-36324-3. Full text in Research Archive Show summary

  Abstract Genetically encoded Ca 2+ indicators (GECIs) are widely used to measure neural activity. Here, we explore the use of systemically administered PHP.eB AAVs for brain-wide expression of GECIs and compare the expression properties to intracerebrally injected AAVs in male mice. We show that systemic administration is a promising strategy for imaging neural activity. Next, we establish the use of EE-RR- (soma) and RPL10a (Ribo) soma-targeting peptides with the latest jGCaMP and show that EE-RR-tagged jGCaMP8 gives rise to strong expression but limited soma-targeting. In contrast, Ribo-tagged jGCaMP8 lacks neuropil signal, but the expression rate is reduced. To combat this, we modified the linker region of the Ribo-tag (RiboL1-). RiboL1-jGCaMP8 expresses faster than Ribo-jGCaMP8 but remains too dim for reliable use with systemic virus administration. However, intracerebral injections of the RiboL1-tagged jGCaMP8 constructs provide strong Ca 2+ signals devoid of neuropil contamination, with remarkable labeling density.

• Lepperød, Mikkel Elle; Christensen, Ane Charlotte; Lensjø, Kristian Kinden; Buccino, Alessio Paolo; Yu, Jai & Fyhn, Marianne [Show all 7 contributors for this article] (2021). Optogenetic pacing of medial septum parvalbumin-positive cells disrupts temporal but not spatial firing in grid cells. Science Advances. 7(19). doi: 10.1126/sciadv.abd5684. Full text in Research Archive Show summary

  Grid cells in the medial entorhinal cortex (MEC) exhibit remarkable spatial activity patterns with spikes coordinated by theta oscillations driven by the medial septal area (MSA). Spikes from grid cells progress relative to the theta phase in a phenomenon called phase precession, which is suggested as essential to create the spatial periodicity of grid cells. Here, we show that optogenetic activation of parvalbumin-positive (PV+) cells in the MSA enabled selective pacing of local field potential (LFP) oscillations in MEC. During optogenetic stimulation, the grid cells were locked to the imposed pacing frequency but kept their spatial patterns. Phase precession was abolished, and speed information was no longer reflected in the LFP oscillations but was still carried by rate coding of individual MEC neurons. Together, these results support that theta oscillations are not critical to the spatial pattern of grid cells and do not carry a crucial velocity signal.

• Christensen, Ane Charlotte; Lensjø, Kristian Kinden; Lepperød, Mikkel Elle; Dragly, Svenn-Arne; Sutterud, Hallvard & Blackstad, Jan Sigurd [Show all 8 contributors for this article] (2021). Perineuronal nets stabilize the grid cell network. Nature Communications. 12. doi: 10.1038/s41467-020-20241-w. Full text in Research Archive Show summary

  Grid cells are part of a widespread network which supports navigation and spatial memory. Stable grid patterns appear late in development, in concert with extracellular matrix aggregates termed perineuronal nets (PNNs) that condense around inhibitory neurons. It has been suggested that PNNs stabilize synaptic connections and long-term memories, but their role in the grid cell network remains elusive. We show that removal of PNNs leads to lower inhibitory spiking activity, and reduces grid cells’ ability to create stable representations of a novel environment. Furthermore, in animals with disrupted PNNs, exposure to a novel arena corrupted the spatiotemporal relationships within grid cell modules, and the stored representations of a familiar arena. Finally, we show that PNN removal in entorhinal cortex distorted spatial representations in downstream hippocampal neurons. Together this work suggests that PNNs provide a key stabilizing element for the grid cell network.

• Sugden, Arthur; Zaremba, Jeffrey; Sugden, Lauren A; Maguire, Kelly; Lutas, Andrew & Ramesh, Rohan [Show all 10 contributors for this article] (2020). Cortical reactivations of recent sensory experiences predict bidirectional network changes during learning. Nature Neuroscience. ISSN 1097-6256. 23, p. 981–991. doi: 10.1038/s41593-020-0651-5. Full text in Research Archive
• Christensen, Ane Charlotte; Lepperød, Mikkel; Lensjø, Kristian Kinden; Dragly, Svenn-Arne; Blackstad, Jan Sigurd Beddari & Fyhn, Marianne [Show all 7 contributors for this article] (2019). Perineuronal nets stabilize the grid cell network. BioRxiv. ISSN 0362-4331. doi: 10.1101/796342. Full text in Research Archive
• Thompson, Elise Holter; Lensjø, Kristian Kinden; Wigestrand, Mattis B; Malthe-sørenssen, Anders; Hafting, Torkel & Fyhn, Marianne (2018). Removal of perineuronal nets disrupts recall of a remote fear memory. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 115(3), p. 607–612. doi: 10.1073/pnas.1713530115. Full text in Research Archive Show summary

  Throughout life animals learn to recognize cues that signal danger and instantaneously initiate an adequate threat response. Memories of such associations may last a lifetime and far outlast the intracellular molecules currently found to be important for memory processing. The memory engram may be supported by other more stable molecular components, such as the extracellular matrix structure of perineuronal nets (PNNs). Here, we show that recall of remote, but not recent, visual fear memories in rats depend on intact PNNs in the secondary visual cortex (V2L). Supporting our behavioral findings, increased synchronized theta oscillations between V2L and basolateral amygdala, a physiological correlate of successful recall, was absent in rats with degraded PNNs in V2L. Together, our findings suggest a role for PNNs in remote memory processing by stabilizing the neural network of the engram.

• Rowlands, Daire; Lensjø, Kristian Kinden; Dinh, Tovy; Yang, Sujeon; Andrews, Melissa & Hafting, Torkel [Show all 9 contributors for this article] (2018). Aggrecan directs extracellular matrix mediated neuronal plasticity. Journal of Neuroscience. ISSN 0270-6474. 38(47), p. 10102–10113. doi: 10.1523/JNEUROSCI.1122-18.2018. Full text in Research Archive Show summary

  In the adult brain, the extracellular matrix (ECM) influences recovery after injury, susceptibility to mental disorders, and is in general a strong regulator of neuronal plasticity. The proteoglycan aggrecan is a core component of the condensed ECM structures termed perineuronal nets (PNNs), and the specific role of PNNs on neural plasticity remains elusive. Here, we genetically targeted the Acan gene encoding for aggrecan utilizing a novel animal model. This allowed for conditional and targeted loss of aggrecan in vivo, which ablated the PNN structure and caused a shift in the population of parvalbumin expressing inhibitory interneurons towards a high plasticity state. Selective deletion of the Acan gene in the visual cortex of male adult mice reinstated juvenile ocular dominance plasticity, which was mechanistically identical to critical period plasticity. Brain-wide targeting improved object recognition memory.

• Lensjø, Kristian Kinden; Lepperød, Mikkel Elle; Dick, Gunnar; Hafting, Torkel & Fyhn, Marianne (2017). Removal of perineuronal nets unlocks juvenile plasticity through network mechanisms of decreased inhibition and increased gamma Activity. Journal of Neuroscience. ISSN 0270-6474. 37(5), p. 1269–1283. doi: 10.1523/JNEUROSCI.2504-16.2016. Full text in Research Archive
• Lensjø, Kristian Kinden; Christensen, Ane Charlotte; Tennøe, Simen; Fyhn, Marianne & Hafting, Torkel (2017). Differential Expression and Cell-Type Specificity of Perineuronal Nets in Hippocampus, Medial Entorhinal Cortex and Visual Cortex Examined in the Rat and Mouse. eNeuro. 4(3), p. 1–18. doi: 10.1523/ENEURO.0379-16.2017. Full text in Research Archive Show summary

  Perineuronal nets (PNNs) are specialized extracellular matrix (ECM) structures that condense around the soma and proximal dendrites of subpopulations of neurons. Emerging evidence suggests that they are involved in regulating brain plasticity. However, the expression of PNNs varies between and within brain areas. A lack of quantitative studies describing the distribution and cell-specificity of PNNs makes it difficult to reveal the functional roles of PNNs. In the current study, we examine the distribution of PNNs and the identity of PNN-enwrapped neurons in three brain areas with different cognitive functions: the dorsal hippocampus, medial entorhinal cortex (mEC) and primary visual cortex (V1). We compared rats and mice as knowledge from these species are often intermingled. The most abundant expression of PNNs was found in the mEC and V1, while dorsal hippocampus showed strikingly low levels of PNNs, apart from dense expression in the CA2 region. In hippocampus we also found apparent species differences in expression of PNNs. While we confirm that the PNNs enwrap parvalbumin-expressing (PV+) neurons in V1, we found that they mainly colocalize with excitatory CamKII-expressing neurons in CA2. In mEC, we demonstrate that in addition to PV+ cells, the PNNs colocalize with reelin-expressing stellate cells. We also show that the maturation of PNNs in mEC coincides with the formation of grid cell pattern, while PV+ cells, unlike in other cortical areas, are present from early postnatal development. Finally, we demonstrate considerable effects on the number of PSD-95-gephyrin puncta after enzymatic removal of PNNs.

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• Rogge, Frederik Sebastian; Lensjø, Kristian; Nymoen, Ingeborg; Grødem, Sverre & Fyhn, Marianne (2025). Visual cue representations in the postrhinal and medial entorhinal cortex during spatial navigation. Full text in Research Archive
• Nymoen, Ingeborg; Rogge, Frederik Sebastian; Grødem, Sverre; Lepperød, Mikkel Elle; Hafting, Torkel & Lensjø, Kristian [Show all 7 contributors for this article] (2024). Visual associative learning in the medial entorhinal cortex. Full text in Research Archive
• Rogge, Frederik Sebastian; Nymoen, Ingeborg; Lepperød, Mikkel Elle; Hafting, Torkel; Fyhn, Marianne & Lensjø, Kristian (2022). Learning flexibility in parahippocampal networks. doi: https:/fensforum.org/wp-content/uploads/2023/01/FENS2022.pdf. Full text in Research Archive Show summary

  Mammals show remarkable flexibility of behaviors, and have the ability to abstract specific rules and learning sets into generalized low dimensional structures that can be applied in new conditions. Recent work suggests that this generalization could take place in parahippocampal regions, in particular in the entorhinal cortex (EC). Here, the medial part (MEC) seems to extract the structure of state space irrespective of modality (e.g. spatial or sound). The lateral part (LEC) receives input about complex features of objects and multimodal sensory information from association cortices, including the postrhinal cortex (POR). This puts the EC in a unique position to function as an integration center for higher order representations. To investigate the role of the entorhinal cortex in abstracting and generalizing task content, we have established a set of simple association tasks for mice that enable both rule switching and change of sensory modality. We train mice in these tasks over multiple sessions and record large neuronal populations in the EC during and after training using two-photon imaging. To this end, we utilize custom right-angle prism assemblies that cover either the MEC, or POR and LEC. We hypothesize that both MEC and LEC will display learning-induced changes in the low dimensional neural representations over time, with consistent structures that are used and transferred across different tasks. Our preliminary data from mice trained in a visual association task indicate that neurons in both regions develop representations of task structure with training.

• Schlegel, Ulrike; Hjallar, Viktor A.; Lensjø, Kristian; Uggerud, Ida Margrethe; Bjaalie, Jan G. & Hvoslef-Eide, Martha [Show all 8 contributors for this article] (2022). Mapping of parahippocampal and visual neural networks in mice: Preliminary evidence for feedback projections from perirhinal cortex to visual areas. Full text in Research Archive Show summary

  Feedback projections from higher-order processing areas to lower-order areas within the visual system havebeen observed in several species. While much is known about the function of feedforward connections in thevisual processing pathway, feedback connections are not as well studied. They are thought to cause behaviorssuch as (selective) attention or expectations, but the exact mechanism and underlying neural connectivity isstill unknown. The perirhinal cortex (PRH) forms the intersection between perceptual and mnemonic areas ofthe visual processing pathway. Evidence from rats, monkeys and humans suggests that it is involved in bothobject memory and perceptual tasks, which is reflected in its connectivity. PRH forms numerous feedforwardand feedback projections with other areas of the visual processing pathway. However, little is known about thefunction and organization of feedback projections from PRH, and other parahippocampal regions, to visualareas in mice. Given the widespread availability of genetic and molecular tools, novel opportunities toinvestigate the function of these feedback projections would be enabled by mapping them in mice. Here wepresent preliminary data from anterograde and retrograde tract tracing experiments showing feedbackprojections from PRH, and other parahippocampal regions, to visual areas. We have found first evidence forfeedback projections from PRH to lower-order visual areas that were assumed to be exclusive to higher-developed animals such as monkeys or humans. Further, we have identified feedback projections from otherparahippocampal regions with specific subregional distribution.

• Røe, Malin Benum; Aasebø, Ida Elisabeth Jørgensen; Mobarhan, Milad; Lensjø, Kristian Kinden; Einevoll, Gaute & Hafting, Torkel [Show all 7 contributors for this article] (2019). Stable orientation tuning in the freely moving rat: Movement-robust orientation-selective neurons in the deep layers of the primary visual cortex. Full text in Research Archive
• Røe, Malin Benum; Aasebø, Ida Elisabeth Jørgensen; Mobarhan, Milad; Lensjø, Kristian Kinden; Einevoll, Gaute & Hafting, Torkel [Show all 7 contributors for this article] (2019). Stable orientation tuning in the freely moving rat: Movement-robust orientation-selective neurons in the deep layers of the primary visual cortex. Full text in Research Archive
• Røe, Malin Benum; Aasebø, Ida Elisabeth Jørgensen; Mobarhan, Milad; Lensjø, Kristian Kinden; Einevoll, Gaute & Hafting, Torkel [Show all 7 contributors for this article] (2018). Movement-resistant orientation selectivity of cells in the deep layers of the rat visual cortex. Full text in Research Archive
• Røe, Malin Benum; Aasebø, Ida Elisabeth Jørgensen; Mobarhan, Milad; Lensjø, Kristian Kinden; Einevoll, Gaute & Hafting, Torkel [Show all 7 contributors for this article] (2018). Stable orientation tuning in the freely moving rat: Movement-robust orientation selective neurons in the deep layers of the primary visual cortex. Full text in Research Archive
• Aasebø, Ida Elisabeth Jørgensen; Røe, Malin Benum; Mobarhan, Milad; Lensjø, Kristian Kinden; Stöber, Tristan Manfred & Einevoll, Gaute [Show all 8 contributors for this article] (2018). Orientation selectivity in the freely moving rat: Movement-robust orientation-selectivity (MROS) of units in the deep layers of the rat visual cortex. Full text in Research Archive
• Grødem, Sverre; Sandvik, Guro Katrine; Hazen, Jennifer; Lensjø, Kristian Kinden; Hafting, Torkel & Fyhn, Marianne (2018). A CRISPR-Cas9 platform for genetic perturbations of brain extracellular matrix regulators in vivo. Full text in Research Archive
• Røe, Malin Benum; Aasebø, Ida Elisabeth Jørgensen; Mobarhan, Milad; Lensjø, Kristian Kinden; Stöber, Tristan Manfred & Einevoll, Gaute [Show all 8 contributors for this article] (2018). Stable orientation tuning in the freely moving rat: Movement-robust orientation-selective neurons in the deep layers of the primary visual cortex. Full text in Research Archive
• Lensjø, Kristian Kinden; Rowlands, Daire; Dinh, Tovy; Thompson, Elise Holter; Andrews, Melissa & Hafting, Torkel [Show all 9 contributors for this article] (2018). Conditional knock-out of the Acan gene removes perineuronal nets in adult mice and induces life-long brian plasticity. Full text in Research Archive
• Dinh, Tovy; Lensjø, Kristian Kinden; Lanton, Rune Alexander; Dick, Gunnar; Fyhn, Marianne & Hafting, Torkel (2017). Increased ocular dominance plasticity in adult visual cortex after genetic knock out of aggrecan, an essential component of perineuronal nets. Full text in Research Archive
• Aasebø, Ida E. J.; Mobarhan, Milad; Røe, Malin Benum; Lensjø, Kristian Kinden; Einevoll, Gaute & Hafting, Torkel [Show all 7 contributors for this article] (2017). Movement-resistant orientation-selective units in the deep layers of the visual cortex. Full text in Research Archive
• Christensen, Ane Charlotte; Lensjø, Kristian Kinden; Lepperød, Mikkel Elle; Fyhn, Marianne & Hafting, Torkel (2017). The role of extracellular matrix molecules for spatial representations in medial entorhinal cortex. Full text in Research Archive
• Thompson, Elise Holter; Lensjø, Kristian Kinden; Wigestrand, Mattis B; Hafting, Torkel; Malthe-Sørenssen, Anders & Fyhn, Marianne (2017). The perineuronal nets in the lateral secondary visual cortex are essential for remote visual fear memory. Full text in Research Archive
• Blackstad, Jan Sigurd; Christensen, Ane Charlotte; Lensjø, Kristian Kinden; Hafting, Torkel & Fyhn, Marianne (2016). Involvement of perineuronal nets in spatial information transfer between the entorhinal cortex and hippocampus. Full text in Research Archive
• Lepperød, Mikkel Elle; Wigestrand, Mattis B; Frey, M.M.; Lensjø, Kristian Kinden; Einevoll, Gaute & Solstad, Trygve [Show all 8 contributors for this article] (2016). Role of input-specific perturbations of medial septal projections to the grid cell network. Full text in Research Archive
• Lepperød, Mikkel Elle; Wigestrand, Mattis B; Lensjø, Kristian Kinden; Frey, M.M.; Dragly, Svenn-Arne & Einevoll, Gaute [Show all 9 contributors for this article] (2016). Grid cell network resilient to input-specific medial septum perturbations. Full text in Research Archive
• Lepperød, Mikkel Elle; Wigestrand, Mattis B; Frey, Mina Martine; Lensjø, Kristian Kinden; Einevoll, Gaute & Solstad, Trygve [Show all 8 contributors for this article] (2016). On the role of input-specific perturbations of medial septal projections to the grid cell network. Full text in Research Archive
• Blackstad, Jan Sigurd; Christensen, Ane Charlotte; Lensjø, Kristian Kinden; Hafting, Torkel & Fyhn, Marianne (2016). Involvement of perineuronal nets in spatial information transfer between the entorhinal cortex and hippocampus. Full text in Research Archive
• Thompson, Elise Holter; Lensjø, Kristian Kinden; Wigestrand, Mattis B; Hafting, Torkel; Fyhn, Marianne & Malthe-Sørenssen, Anders (2016). The perineuronal nets in the lateral secondary visual cortex are essential for remote visual memory. Full text in Research Archive
• Røe, Malin Benum; Aasebø, Ida E. J.; Lensjø, Kristian Kinden; Hafting, Torkel & Fyhn, Marianne (2016). Orientation selective cells in layer six of the primary visual cortex are resistant to the animal's movement. Full text in Research Archive
• Thompson, Elise Holter; Lensjø, Kristian Kinden; Wigestrand, Mattis B; Hafting, Torkel & Fyhn, Marianne (2016). The perineuronal nets in the lateral secondary visual cortex and their impact on remote visual fear memory. Full text in Research Archive
• Lensjø, Kristian Kinden; Lepperød, Mikkel Elle; Dick, Gunnar; Hafting, Torkel & Fyhn, Marianne (2016). Removal of perineuronal nets affects information processing and plasticity in the primary visual cortex. Full text in Research Archive
• Lepperød, Mikkel Elle; Lensjø, Kristian Kinden; Christensen, Ane Charlotte; Fyhn, Marianne; Hafting, Torkel & Einevoll, Gaute (2015). Building an entorhinal cortex network. Full text in Research Archive
• Christensen, Ane Charlotte; Lensjø, Kristian Kinden; Lepperød, Bjørn Mikkel Elle; Fyhn, Marianne & Hafting, Torkel (2015). The role of extracellular matrix molecules for spatial representations and plasticity in entorhinal cortex. Full text in Research Archive
• Lensjø, Kristian Kinden; Lepperød, Bjørn Mikkel Elle; Dick, Gunnar; Hafting, Torkel & Fyhn, Marianne (2015). Removal of perineuronal nets in the visual cortex leads to a reduced inhibition and mimics critical period plasticity. Full text in Research Archive
• Hafting, Torkel; Lensjø, Kristian Kinden; Christensen, Ane Charlotte; Dick, Gunnar & Fyhn, Marianne (2014). Perineuronal nets, plasticity and information-processing in visual cortex, medial entorhinal cortex and hippocampus. Full text in Research Archive
• Lensjø, Kristian Kinden; Dick, Gunnar; Fyhn, Torkel Hafting & Fyhn, Marianne (2013). Cortical processing in awake, behaving rats after removal of perineuronal nets. Full text in Research Archive
• Aasebø, Ida E. J.; Norheim, Eivind Skjønsberg; Lensjø, Kristian Kinden; Fyhn, Marianne & Fyhn, Torkel Hafting (2013). The effect of anesthesia on activity and modulation of visually responsive neurons in cortical and subcortical areas. Full text in Research Archive
• Rogge, Frederik Sebastian; Fyhn, Marianne; Malthe-Sørenssen, Anders; Lepperød, Mikkel Elle & Lensjø, Kristian (2026). Normative and Experimental Analyses of Learning-Dependent Representations in the Hippocampal-Parahippocampal System. Universitetet i Oslo. Full text in Research Archive Show summary

  The brain is thought to build a cognitive map of both physical and abstract spaces, helping us navigate the world, organize knowledge, and form new memories. In this thesis, I investigated key brain subregions to uncover the principles underlying the emergence of neural representations. I focused on the general properties of the neural code, how visual inputs are integrated, and how these representations reorganize through learning. To address these questions, I combined large-scale chronic two-photon calcium imaging in mice with normative modeling in artificial neural networks. We show that neurons in the medial entorhinal cortex (MEC) develop task-relevant tuning during learning of a purely visual association task, pointing to a broader role beyond its classical link to spatial coding. In parallel, selective disruption of specific neuron types in the postrhinal cortex (POR) impaired learning of the same task, demonstrating their causal contribution. Furthermore, using artificial neural networks, we uncovered computational principles governing how spatial representations emerge and transform. Finally, we revealed dissociable contributions of POR and MEC to visually guided navigation, highlighting their distinct roles. Together, these results shed new light on the emergence of neural representations in different brain regions and their transformation through learning.

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