Mark joined the faculty at MIT in 2015 and was promoted to AWOT in 2020. He became Graduate Officer in 2021. He received his B.A. in biology from Reed College in Portland, OR and his Ph.D. from the University of Texas at Austin. Prior to joining MIT, he was a postdoctoral researcher at the Howard Hughes Medical Institute’s Janelia Research Campus in Ashburn, VA.
Our laboratory studies how the biophysical features of individual neurons endow neural circuits with powerful processing capabilities, ultimately facilitating the complex computations required to drive adaptive behavior. A principal focus of our work is the role of dendrites, the elaborate tree-like structures where neurons receive the vast majority of afferent input. The spatial arrangement of synaptic contacts on dendrites and the interaction of various biophysical mechanisms enable complex integration of synaptic inputs – our hypothesis is that circuit-level computations are built out of these fundamental operations.
BIOPHYSICS & SINGLE-CELL COMPUTATION
The morphological features and local ion channel mechanisms in specific dendritic compartments strongly influence how neurons integrate their inputs. We combine brain slice electrophysiology, two-photon imaging, and biophysical modeling to investigate the rules and mechanisms supporting different forms of input-output processing across mammalian species.
NEURONAL COMPUTATION IN THE BEHAVING ANIMAL
How do biophysical mechanisms influence circuit-level computation during behavior? To address this question, we combine 2-photon imaging and multi-unit electrophysiological recording techniques with novel rodent behavioral paradigms to measure the activity of neuronal populations including subcellular compartments. This allows us to evaluate the engagement of dendritic mechanisms as a function of circuit dynamics during complex behaviors. These experiments are complemented by detailed anatomical and single-cell physiological investigations in brain slices.
Head direction is critical for efficient navigation and provides an experimentally tractable system with which to study multimodal integration in neural circuits. We use state-of-the-art chronic tetrode implants to record HD activity while mice perform goal-directed navigation in darkness and reorient to visual landmarks. These experiments are combined with anatomical, physiological, and optogenetic techniques, as well as novel behavioral and computational methods, to dissect the cellular and circuit architecture of head direction representations.
9.17 Systems Neuroscience Laboratory
Francioni V, Harnett MT (2021) Rethinking Single Neuron Electrical Compartmentalization: Dendritic Contributions to Network Computation In Vivo. Neuroscience. PMID 34116137
Kim T, Chaloner FA, Cooke SF, Harnett MT, Bear MF (2020) Opposing Somatic and Dendritic Expression of Stimulus-Selective Response Plasticity in Mouse Primary Visual Cortex. Front Cell Neuroscience.
Fischer LF, Mojica Soto-Albors R, Buck F, Harnett MT (2020) Representation of visual landmarks in retrosplenial cortex. Elife. 9. PMID 32154781
Newman JP, Voigts J, Borius M, Karlsson M, Harnett MT, Wilson MA (2020) Twister3: a simple and fast microwire twister. Journal of Neural Engineering. PMID 32074512
Voigts J, Newman JP, Wilson MA, Harnett MT (2020) An easy-to-assemble, robust, and lightweight drive implant for chronic tetrode recordings in freely moving animals. Journal of Neural Engineering.
Voigts J, Harnett MT (2020) Somatic and dendritic encoding of spatial variables in retrosplenial cortex differs during 2D navigation. Neuron 105(2):237-245
Beaulieu-Laroche L, Toloza EHS, Brown NJ, Harnett MT (2019). Widespread and highly correlated somato-dendritic activity in cortical layer 5 neurons. Neuron
Ranganathan GN, Apostolides PF, Harnett MT, Xu NL, Druckmann S, Magee JC (2018). Active dendritic integration and mixed neocortical network representations during an adaptive sensing behavior. Nature Neuroscience 21(11):1583-90
Beaulieu-Laroche L, Toloza EHS, van der Goes MS, Lafourcade M, Barnagian D, Williams ZM, Eskandar EN, Frosch MP, Cash SS, Harnett MT (2018). Enhanced dendritic compartmentalization in human cortical neurons. Cell 175(3):643-651
Beaulieu-Laroche L & Harnett MT (2018). Dendritic spines prevent synaptic voltage clamp. Neuron 97(1):75-82
Shin Yim Y, Park A, Berrios J, Lafourcade M, Pascual LM, Soares N, Yeon Kim J, Kim S, Kim H, Waisman A, Littman DR, Wickersham IR, Harnett MT, Huh JR, Choi GB (2017). Reversing behavioural abnormalities in mice exposed to maternal inflammation. Nature 549(7673):482-487