Throughout his career Karl has worked on elucidating the neural substrates of  sleep either using  humans or rodent and zebrafish as models. The core questions revolve on elucidating the neural substrates of sleep in this teleost fish, comparing them to what is known in mammals; revealing the state-dependent genetic expression in zebrafish and to clarify the role of sleep in various aspects of neural plasticity.  Over the years the focus has shifted towards using zebrafish for various CNS disease modelling and drug discovery. The core methods we employ in the lab include automated behavioral analysis, basic genetics, metabolomics, histology and in vivo/in vitro electrophysiology. 


Sveinsdóttir HS, Christensen C, Þorsteinsson H, Lavalou P, Parker MO, Shkumatava A, Norton WHJ, Andriambeloson E, Wagner S, Karlsson KÆ. Novel non-stimulants rescue hyperactive phenotype in an adgrl3.1 mutant zebrafish model of ADHD. Neuropsychopharmacology. 2022 Nov 18. doi: 10.1038/s41386-022-01505-z. Epub ahead of print. PMID: 36400921.

Sveinsdóttir HS, Decker A, Christensen C, Lucena PB, Þorsteinsson H, Richert E, Maier VH, Cornell R, Karlsson KÆ. Motility phenotype in a zebrafish vmat2 mutant. PLoS One. 2022 Jan 5;17(1):e0259753. doi: 10.1371/journal.pone.0259753. PMID: 34986152; PMCID: PMC8730441.

Paul R. Manger, Nina Patzke, Muhammad A. Spocter, Adhil Bhagwandin, Karl Æ. Karlsson, Mads F. Bertelsen, Abdulaziz N. Alagaili, Nigel C. Bennett, Osama B. Mohammed, Suzana Herculano-Houzel, Patrick R. Hof, Kjell Fuxe. Amplification of potential thermogenetic mechanisms in cetacean brains compared to artiodactyl brains. Scientific Reports. 11, Article number: 5486 (2021

Christensen C, Þorsteinsson H, Maier VH, Karlsson KÆ. Multi-parameter Behavioral Phenotyping of the MPP+ Model of Parkinson’s Disease in Zebrafish. Front Behav Neurosci. 2020 Dec 18;14:623924. doi: 10.3389/fnbeh.2020.623924. PMID: 33390914; PMCID: PMC7775599.

Transient knock-down of kcna2 reduces sleep in larval zebrafish. S Srdanović, H Þorsteinsson, Þ Friðriksson, SÓ Pétursson, VH Maier & Karlsson, K.Æ. Behavioural Brain Research. (2017) 326, 13-21.

Organization of the sleep‐related neural systems in the brain of the minke whale (Balaenoptera acutorostrata). (2015) Leigh-Ann Dell, Karl Æ. Karlsson, Muhammad A. Spocter, Jerome M. Siegel and Paul R. Manger. Journal of Comparative Neuroanatomy DOI 10.1002/cne.23931

Orexinergic bouton density is lower in the cerebral cortex of cetaceans compared to artiodactyls. (2015) Nina Patzke, Muhammad A. Spocter, Karl Æ. Karlsson, Mads F. Bertelsen, Mark Haagensen, Richard Chawana, Sonja Streicher, Consolate Kaswera, Emmanuel Gilissen, Abdulaziz N. Alagaili, Osama B. Mohammed, Roger L. Reep, Nigel C. Bennett, Jerry M. Siegel, Amadi O. Ihunwo, Paul R. Manger. Journal of chemical neuroanatomy 68, 61-76. 

Absence of rapid eye movements during sleep in adult zebrafish. Árnason, B.B, Þorsteinsson, H. & Karlsson, K.Æ.(2015). Behavioural Brain Research 15; 291, 189-194.

Sigurgeirsson, B., Þorsteinsson, H., Sigmundsdóttir, S., Lieder, R., Sveinsdóttir, H., Halldórsson, B.V. & Karlsson, K.Æ. Sleep-wake modulation of gene expression in zebrafish. (2013). Behavioural Brain Research. 256: 377-390

Nina Patzke, Muhammad A. Spocter, Karl Æ. Karlsson, Mads F. Bertelsen, Mark Haagensen, Richard Chawana, Sonja Streicher, Consolate Kaswera, Emmanuel Gilissen, Abdulaziz N. Alagaili, Osama B. Mohammed, Roger L. Reep, Nigel C. Bennett, Jerry M. Siegel, Amadi O. Ihunwo, Paul R. Manger. (2013).
In contrast to many other mammals, cetaceans have relatively small hippocampi that appear to lack adult neurogenesis. Brain Structure and Function. DOI 10.1007/s00429-013-0660-1

Sorribes, A., Þorsteinsson, H., Arnardóttir, H., Jóhannesdóttir, I., de Polavieja, G. & Karlsson, K.Æ.
The ontogeny of sleep-wake cycles in zebrafish: a comparison to humans. Frontiers in Neural Circuits. Vol 7, Article 178 1-13

Ashley M. Blouin, Itzhak I. Fried, Charles L. Wilson, Richard J. Staba, Eric J. Behnke, Hoa A. Lam, Nigel T. Maidment, Karl Æ. Karlsson, Jennifer Lapierre & Jerome M. Siegel. Hypocretin and melanin concentrating hormone levels in humans: Strong linkage to emotion and social interaction. Nature Communication, 4, 1547,  doi: 10.1038/ncomms2461

Vargas, R., Þorsteinsson, H. & Karlsson, K.Æ. (2011). Spontaneous neural activity of the anterodorsal lobe and entopeduncular nucleus in adult zebrafish: a putative homologue of hippocampal sharp waves. Behavioural Brain Research, doi:10.1016/j.bbr.2011.12.025

Sigurgeirsson, B., Þorsteinsson, H., Arnardóttir, H., Jóhannesdóttir, I. & Karlsson K.Æ. (2011). Effects of modafinil on sleep–wake cycles in larval zebrafish. Zebrafish. doi:10.1089/zeb.2011.0708

Vargas, R., Jóhannesdóttir, I.Þ., Sigurgeirsson, B., Þorsteinsson H. & Karlsson K.Æ. (2011). The zebrafish brain in research and teaching: a simple in vivo and in vitro model for the study of spontaneous neural activity.  Advances in Physiology Education 35 (2), 188-196.

Arnardóttir, H., Þorsteinsson, H. & Karlsson, K.Æ. (2010). Dynamics of sleep–wake cyclicity at night across the human lifespan. Frontiers of Neurology. Front. Neur. 1:156. doi: 10.3389/fneur.2010.00156 2010.

Karlsson, K. Æ., Arnardóttir, H., Robinson, S. R. & Blumberg, M. S. (2010). Dynamics of sleep–wake cyclicity across the fetal period in sheep (Ovis aries). Developmental psychobiology 53 (1), 89-95.

Þorsteinsson, H., Reynisson, H.M., Sigurðardóttir, L.Ý., Dagbjartsson, A., & Karlsson, K. Æ. (2010). Behavioral correlates of direct current-coupled electrographic activity in premature infants. Behavioural brain research. Vol, 211(1), 11-15.

Karlsson, K. Æ., Windischberger, C., Gerstl, F., Mayr, W., Siegel, J.M., Moser, E.(2010). Modulation of hypothalamus and amygdalar activation levels with stimulus valence.  Neuroimage, Vol 51 (1), 324-328.

Þorsteinsson, H. & Karlsson, K.Æ. (2009). Is Sleep Beyond Our Control? The Open Sleep Journal Vol 2, 48-55.

Mohns, E. J., Karlsson, K. Æ., & Blumberg, M.S. (2007). Developmental emergence of transient and persistent hippocampal events and oscillations and their association with infant seizure susceptibility. European Journal of Neuroscience. Vol 26 (10), 2719-2730.

Blumberg, M.S., Karlsson, K. Æ. & Seelke, A.M. (2007). Sleep, development and human health. Sleep. Vol 30, 5, 549-550.

Karlsson, K.Æ.,Vianna Di Prisco, G., Mohns, E.J. & Blumberg M.S. (2006). On the Co-expression of Startles and Hippocampal Sharp Waves in Newborn rats. Hippocampus. Vol, 11, 959-965.

Mohns, E. J., Karlsson, K. Æ., & Blumberg, M.S. (2006). The ventrolateral preoptic area and basal forebrain play opposing roles in the descending modulation of sleep-wake cyclicity in infant rats. European Journal of Neuroscience. Vol 20, 1301-1310.

Blumberg, M.S., Seelke, A. M., Lowen, S.B., & Karlsson, K. Æ. (2005). Dynamics of Sleep-Wake Cyclicity in Developing Rats. Proceedings of the National Academy of Sciences. Vol, 102, 14860-14864.

Seelke, A. M., Karlsson, K. Æ., Gall, A. J. & Blumberg M. S. (2005). Extraocular Muscle Activity, Rapid Eye Movements, and the Development of Active and Quiet Sleep. European Journal of Neuroscience. 22, 911-920.

Karlsson, K. Æ., Gall, A. J. Mohns, E. J. & Blumberg, M.S. (2005). The Neural Substrates of Infant Sleep in Rats. Public Library of Science Biology. 3(5): e143

Karlsson, K. Æ. & Blumberg, M.S. (2005). Active Control of Atonia in Week-Old Rats. Neuroscience. 130, 275-283.

Blumberg, M.S., Karlsson, K. Æ., Seelke, A.M.H. & Mohns, E. (2004). The Ontogeny of Mammalian Sleep: A Reply to Frank and Heller (2003). Journal of Sleep Research, 14, 91-101.

Karlsson, K. Æ. & Blumberg, M.S. (2004). Temperature-Induced Reciprocal Activation of Hippocampal Field Activity in vivo. Journal of Neurophysiology, 91, 583-588.

Karlsson, K. Æ., Kreider, J.C. & Blumberg, M.S. (2004). Hypothalamic Contributions to Sleep-Wake Cycle Development. Neuroscience, 123, 575-582.

Karlsson, K. Æ. & Blumberg, M. S. (2003). Hippocampal Theta in the Newborn Rat is Revealed Under Conditions That Promote REM sleep. The Journal of Neuroscience, 23(4) 1114-1118.

Karlsson, K. Æ., & Blumberg, M. S. (2002). Union of the State: Myoclonic Twitching is Coupled with Muscle Atonia in Infant Rats. Behavioral Neuroscience, 116, 912-917.