Cortical circuits underlying social and spatial exploration in rats DISSERTATION zur Erlangung des akademischen Grades D o c t o r r e r u m n a t u r a l i u m (Dr. rer. nat.) im Fach Biologie eingereicht an der Lebenswissenschaftlichen Fakultät der Humboldt-Universität zu Berlin von M.Sc. Christian Laut Ebbesen Präsidentin der Humboldt-Universität zu Berlin Prof. Dr.-Ing. Dr. Sabine Kunst Dekan der Lebenswissenschaftlichen Fakultät Prof. Dr. Bernhard Grimm Gutachter 1. Prof. Matthew Larkum, Ph.D.. Matthew Larkum, Ph.D. 2. Dr. James Poulet Dr . James Poulet 3. Prof. Dr. Michael Brecht Prof. Dr. Michael Brecht Tag der mündlichen Prüfung: 6. Juli 2017 BERLIN SCHOOL OF MIND AND BRAIN berlin Cortical circuits underlying social and spatial exploration in rats Doctoral candidate: Christian Laut Ebbesen Supervisors: Prof. Dr. Michael Brecht Prof. Dr. Gabriel Curio April 2017 Berlin School of Mind and Brain Bernstein Center for Computational Neuroscience Animal Physiology / Systems Neurobiology and Neural Computation Humboldt Universität zu Berlin, Berlin, Germany Ebbesen (2017) Table of Contents 1. Abstract 1 2. Zusammenfassung 3 3. General Introduction & Thesis Outline 4 3.1 General Introduction . 4 3.1.1 Why do we study the brain?. 4 3.1.2 Three heuristics for investigating neural circuits. 4 3.1.3 Neuroethology & functional localization . 5 3.1.4 How should we look a cortical data? . 7 3.2 Thesis Outline. 8 3.2.1 Two investigations into cortical function . 8 3.2.2 Part 1: Parahippocampal cortex and neural circuits underlying spatial exploration 9 3.2.3 Part 2: Motor cortex and neural circuits underlying social exploration . .12 3.3 References. 15 4. Pyramidal and Stellate Cell Specificity of Grid and Border Representations in Layer 2 of Medial Entorhinal Cortex 22 4.1 Introduction. 23 4.2 Results. 23 4.3 Discussion. 28 4.4 Experimental Procedures . .28 4.5 References. 29 4.6 Supplemental Information. 30 5. Functional Architecture of the Rat Parasubiculum 52 5.1 Introduction. 53 5.2 Materials and Methods . .54 5.3 Results. 56 5.4 Discussion. 59 5.5 References. 64 6. Cell Type-Specific Differences in Spike Timing and Spike Shape in the Rat Parasubiculum and Superficial Medial Entorhinal Cortex 66 6.1 Introduction. 68 6.2 Results. 69 6.3 Discussion. 74 6.4 Experimental Procedures . .76 6.5 References. 77 I Ebbesen (2017) 6.6 Supplemental Information. 79 7. Vibrissa motor cortex activity suppresses contralateral whisking behavior 90 7.1 Introduction. 93 7.2 Results. 94 7.3 Discussion. 99 7.4 References. 102 7.5 Figures. 107 7.6 Methods. 120 7.7 Methods References. 128 8. Motor cortex – To act or not to act? 130 8.1 Introduction. 133 8.2 From motor cortex to muscle output . 135 8.3 Inactivation studies: Acting without motor cortex. 142 8.4 Motor cortex – not to act?. 144 8.5 Conclusions. 147 8.6 References. 150 8.7 Figures. 161 9. General Discussion 168 9.1 Parahippocampal cortex and neural circuits underlying spatial exploration . 168 9.1.1 Structure-function relationships in parahippocampal cortex . 168 9.1.2 How are grid cells made? . 168 9.1.3 What does the grid cell system teach us about cortical computation? . 170 9.2 Motor cortex and neural circuits underlying social exploration . 172 9.2.1 What is the function of rat vibrissa motor cortex?. 172 9.2.2 Social computations in sensorimotor cortex. 173 9.3 References. 174 10. Curriculum vitae 182 11. List of publications 184 12. Declaration of contribution 185 13. Acknowledgements 190 PLACER II Ebbesen (2017) List of Figures Figure 1 The cerebral cortex is the outermost cell layers of the mammalian telencephalon.. 5 Figure 2 An example of viewing cortical data in the ‘right’ way? . 7 Figure 3 Schematic showing the location of motor cortex and parahippocampal cortex in the rat brain. 9 Figure 4 Hippocampal place cells. 9 Figure 5 Spatial discharge patterns of neurons in parahippocampal cortex.. 10 Figure 6 Social facial touch. 13 Figure 7 Movement suppression is under-represented in depictions of motor cortex . 14 Figure 8 Graphical abstract outlining the main message of this chapter. .22 Figure 9 A Wistar rat it reins. .90 Figure 10 Modular cytoachitectonics of parahippocampal cortex. 148 Figure 11 Grid-cell-like responses of entorhinal neurons to saccades across a visual scene. 149 Figure 12 What are cortical neurons doing? . 151 III Ebbesen (2017) IV Ebbesen (2017) Declaration I declare that the doctoral thesis entitled Cortical circuits underlying social and spatial exploration in rats represents an original work of the author apart from the references and declared contributions under the provisions § 6 (3) of the doctoral degree regulations, dated 5 March 2015, of the faculty of Life Sciences of Humboldt-Universität zu Berlin. The work involved no collaborations with com- mercial doctoral degree supervisors. I affirm that I have neither applied for nor hold a corresponding doctoral degree and this work has not been submitted in full or part to another academic institution. Further, I acknowledge the doctoral degree regulations which underlie this procedure, and state that I abided by the principles of good academic practice of Humboldt-Universität zu Berlin. Christian Laut Ebbesen, April 2017 V Ebbesen (2017) VI Ebbesen (2017) Abstract 1. Abstract In order to understand how the mammalian brain works, we must investigate how neural activ- ity contributes to cognition and generates complex behavioral output. In this thesis I present work, which focuses on two regions of the cerebral cortex of rats: parahippocampal cortex and motor cortex. In the first part of the thesis we investigate neural circuits in the parasubiculum and the superficial medial enthorhinal cortex, two structures that play a key role in spatial cognition. Briefly, we find that the in these regions, anatomical identity and microcircuit embedding is a major determinant of both spatial discharge patterns (such as the discharge patterns of grid cells, border cells and head-direction cells) and temporal coding features (such as spike bursts, theta-modulation and phase precession). In the second part of the thesis we investigate the activity of neurons in vibrissa motor cortex during complex motor behaviors, which play a vital role in rat ecology: self-initiated bouts of exploratory whisking in air, whisking to touch conspecifics during social interactions and whisking to palpate objects. Briefly, we find that neural activity decreases during whisking behaviors, that microstimula- tion leads to whisker retraction and that pharmacological blockade increases whisker movement. Thus, our observations collectively suggest that a primary role of vibrissa motor cortex activity is to suppress whisking behaviors. The second part of the thesis concludes with a literature review of motor sup- pressive effects of motor cortical activity across rodents, primates and humans to put this unexpected finding in a broader context. 1 Ebbesen (2017) 2 Ebbesen (2017) Zusammenfassung 2. Zusammenfassung Um zu verstehen, wie das Gehirn von Säugetieren funktioniert, untersuchen wir wie neuronale Aktivität einerseits zu Kognition beträgt und andererseits komplexe Verhaltensweisen ermöglicht. Im Fokus dieser Doktorarbeit stehen dabei zwei Regionen der Großhirnrinde der Ratte: der para- hippocampale Cortex und der motorische Cortex. Im ersten Teil haben wir neuronale Schaltkreise im parahippocampalen Cortex und in den oberen Schichten des enthorhinalen Cortex untersucht, während Ratten ihre Umgebung räumlich erkunden. Diese beiden Regionen tragen wesentlich zum Orientierungssinn bei. Dabei haben wir herausgefunden, dass anatomische Identität und Einbindung in den Microschaltkreis einerseits räumliche neuronale Signale, wie zum Beispiel der Aktivität von grid cells, border cells und head-direction cells, bestimmen. Andererseits tragen diese beiden Eigen- schaften auch zur temporalen Präzision neuronaler Signale bei, wie zum Beispiel in Form von spike bursts, theta Modulation und phase precession. Im zweiten Teil dieser Doktorarbeit untersuchen wir die Aktivität von Neuronen im Vibrissen Motorcortex während komplexer Bewegungsabläufe der Schnurrhaare, die dem natürlichen Repertoire der Ratte entstammen: eigeninitiierte Bewegungen in freier Luft, Berührung von Artgenossen zur sozialen Interaktion und das Abtasten von Objekten. Da- bei haben wir herausgefunden, dass neuronale Aktivität im Motorcortex während der Bewegung der Schnurrhaare unterdrückt ist, dass elektrische Microstimulation zum Rückzug der Schnurrhaare führt und, dass pharmakologische Blockade Bewegung der Schnurrhaare fördert. Um diese überraschende Beobachtung in einen breiteren Kontext zu integrieren, endet dieser Teil mit einer Bewertung der Literatur zu der bewegungsunterdrückenden Wirkung von Motorcortex Aktivität bei Nagetieren, Pri- maten und Menschen. 3 Ebbesen (2017) Chapter 2 3. General Introduction & Thesis Outline 3.1 General Introduction 3.1.1 Why do we study the brain? Three major factors make the mammalian forebrain one of the most interesting structures in the universe: a perspective of basic health care, a perspective of introspection and a political perspec- tive. First, a better understanding of the mammalian neurobiology would be immensely helpful in designing novel therapeutic strategies for mental conditions. These conditions have high incidence and major impact on life quality, but presently totally dissatisfactory treatment options (Connell et al., 2014; Diener et al., 1999; Lehman, 1996; WHO, 1995). Thus, advances in this regard would have massive positive