Date: Monday, April 14th at 10AMIn-person Location: 46-3189, McGovern Seminar RoomOn Zoom: https://mit.zoom.us/j/94586137096Title: Top-down and bottom-up interactions for cortical burstingAbstract: High-frequency burst firing occurs throughout the mammalian cortex in vivo, yet both the underlying mechanisms and functional roles of bursts are unclear. Burst firing in brain slices is strongly modulated by the activity of apical dendrites, which branch extensively in layer 1 (L1) and receive long-range inputs from higher-order cortical and thalamic areas. These properties suggest a powerful subcellular substrate by which single pyramidal neurons could multiplex bottom-up and top-down information via L1-independent tonic spikes and L1-dependent bursts, respectively, and have provided a basis for emerging theoretical models of cortical computation and learning. However, our understanding of burst firing and subcellular processing remains critically limited by a lack of evidence in awake animals. It is unclear whether burst firing a) is preferentially recruited by bottom-up versus top-down inputs, and b) requires apical dendritic engagement. To answer these questions, we performed high-density extracellular recordings in primary visual cortex of awake mice while presenting a battery of Gabor (bottom-up) and inverse (top-down) visual stimuli. We report widespread high-frequency bursts in L2/3 and L5 pyramidal neurons. Contrary to expectation, bursts exhibited extremely short response latencies, and were most strongly recruited by Gabor stimuli. We further tested the causal contribution(s) of apical dendrites to burst firing and top-down visual tuning via two optogenetic manipulations: direct L5 apical tuft inhibition and NDNF interneuron activation. Strikingly, L1 inhibition only modestly reduced the burst fraction, and did not differentially affect Gabor vs inverse responses. Taken together, these results challenge prevailing theories of apical dendritic involvement in burst spike generation and feedback visual tuning, and provide new biological constraints for future theoretical and experimental work.

Have some fun(nel) on a tunnel or sun(nel) walk! Join us for a 30-minute volunteer-led walk either through MIT’s famous tunnel system or around Killian Court. As the weather gets warmer, walk leaders may choose to take the group outside. Is the weather warm and you missed the start? Find the group on Killian Court and join in!Location details: Meet in the lobby with the big mirror, right inside the Collier Memorial entrance to Stata. Location photo below.Sun(nel) Walk Leaders will identify themselves by holding a white flag at the meeting location.Prize Drawing: Attend a walk and scan a QR code from the walk leaders to be entered into a drawing for a getfit canvas boat tote bag at the end of the getfit challenge. The more walks you attend, the more entries you get. Winner will be drawn and notified at the end of April. Winner does not need to be a getfit participant.Disclaimer: These walks are led by volunteers. In the rare occasion when a volunteer isn’t able to make it, we will do our best to notify participants. In the event we are unable to notify participants and a walk leader does not show up, we encourage you to walk as much as you feel comfortable doing so. We recommend checking this calendar just before you head out!Getfit is a 12-week fitness challenge for the entire MIT community. These walks are open to the entire MIT community and you do not need to be a current getfit participant to join.

Have some fun(nel) on a tunnel or sun(nel) walk! Join us for a 30-minute volunteer-led walk either through MIT’s famous tunnel system or around Killian Court. As the weather gets warmer, walk leaders may choose to take the group outside. Is the weather warm and you missed the start? Find the group on Killian Court and join in!Location details: Meet in the lobby with the big mirror, right inside the Collier Memorial entrance to Stata. Location photo below.Sun(nel) Walk Leaders will identify themselves by holding a white flag at the meeting location.Prize Drawing: Attend a walk and scan a QR code from the walk leaders to be entered into a drawing for a getfit canvas boat tote bag at the end of the getfit challenge. The more walks you attend, the more entries you get. Winner will be drawn and notified at the end of April. Winner does not need to be a getfit participant.Disclaimer: These walks are led by volunteers. In the rare occasion when a volunteer isn’t able to make it, we will do our best to notify participants. In the event we are unable to notify participants and a walk leader does not show up, we encourage you to walk as much as you feel comfortable doing so. We recommend checking this calendar just before you head out!Getfit is a 12-week fitness challenge for the entire MIT community. These walks are open to the entire MIT community and you do not need to be a current getfit participant to join.

Ten minutes for your mind@2:50 every day at 2:50 pm in multiple time zones:Europa@2:50, EET, Athens, Helsinki (UTC+2) (7:50 am EST) https://us02web.zoom.us/j/88298032734Atlantica@2:50, EST, New York, Toronto (UTC-4) https://us02web.zoom.us/j/85349851047Pacifica@2:50, PST, Los Angeles, Vancouver (UTC=7) (5:50 pm EST) https://us02web.zoom.us/j/85743543699Almost everything works better again if you unplug it for a bit, including your mind. Stop by and unplug. Get the benefits of mindfulness without the fuss.@2:50 meets at the same time every single day for ten minutes of quiet together.No pre-requisite, no registration needed.Visit the website to view all @2:50 time zones each day.at250.org or at250.mit.edu

Talk Title: Activating Metal Sites for Biological Electron TransferWebsite: https://web.stanford.edu/group/solomon/home.html

Marcella Alsan Harvard University Kennedy School of Management