Brain Space Time Podcast

I just visited the ESI SyNC 2024 conference on the topic of "Time in the brain". There, I interviewed Hugo Merchant, an electrophysiologist at UNAM in Juriquilla, Mexico. Hugo works with macaques, who can rhythmically tap their fingers synchronized to a visual or auditory beat. By studying macaque neural activity in dimensionality-reduced spaces, he wants to understand how the brain encodes different time intervals. For an overview of our conversation, see the timestamps below.

Timestamps:

(00:00:00) - Intro

(00:02:57) - Monkeys rhythmic finger tapping

(00:08:27) - Timing network in pre-motor cortex and basal ganglia

(00:12:43) - Circular neural trajectories

(00:16:08) - Mapping latent space to single-cell physiology

(00:20:15) - Experimentally slowing the clock

(00:23:19) - Spatial organization of circuits

(00:27:59) - Error correction & single-trial analyses

(00:38:57) - Bayesian & SNN models

Hugo's Website

Hugo's publications & talks:

Betancourt et al., 2023 - Amodal population clock in the primate medial premotor system for rhythmic tapping paper

Pérez et al., 2023 - Rhythmic tapping to a moving beat: motion kinematics overrules motion naturalness - preprint (Bayesian model)

ESI SyNC 2024 Talk (should be uploaded within a month here)

Other papers/books mentioned:

Shine, 2021 - The thalamus integrates the macrosystems of the brain to facilitate complex, adaptive brain network dynamics paper

Zemlianova et al., 2024 - A Recurrent Neural Network for Rhythmic Timing preprint (SNN model)

For Apple Podcast users, find books/papers links at: https://akseliilmanen.wixsite.com/home/post/pod09

My Twitter @akseli_ilmanen

Email: akseli.ilmanen[at]gmail.com

Brain Space Time Podcast, my blog, other stuff

Music: Space News, License: Z62T4V3QWL

Uri Hasson runs a lab in Princeton, where he investigates the underlying neural basis of natural language acquisition and processing as it unfolds in the real world. As Uri visited Tübingen (where I am doing my master's), we were able to meet in person. Originally, I planned to talk about his idea of temporal receptive windows, and how different brain regions (e.g. default mode network) operate at different timescales. However, we ended up talking more about Wittgenstein, evolution, and ChatGPT. An underlying thread throughout the conversation was that (for both biological and artificial agents), language is not clever symbol and rule manipulation but a brute force fitting to statistics across (Wittgensteinian) 'contexts'. This view is best articulated in Uri's Direct Fit paper. We also connect this to transformers and discuss what's missing in AI. The answer here is multimodal integration, episodic memory, and interactive sociality). At the end, I ask Uri about his 1000 days project, talking to crows, and "understanding" in neuroscience/AI.

For Apple Podcast users, find books/papers links at: https://akseliilmanen.wixsite.com/home/post/pod08

Uri's Website

Twitter: @HassonLab

Uri's publications & talks:

Hasson et al., 2015 - Hierarchical process memory: memory as an integral component of information processing Temporal receptive windows paper

Hasson et al., 2020 - Direct Fit to Nature: An Evolutionary Perspective on Biological and Artificial Neural Networks paper

Yeshurun et al., 2021 - The default mode network: where the idiosyncratic self meets the shared social world paper

Goldstein et al., 2022 - The Temporal Structure of Language Processing in the Human Brain Corresponds to The Layered Hierarchy of Deep Language Models preprint

Nguyen et al., 2022 - Teacher student neural coupling during teaching and learning paper

Goldstein et al., 2022 - Shared computational principles for language processing in humans and deep language models paper

Also mentioned:

Podcast episode with Tony Zador on Genomic Bottlenecks link

My Twitter @akseli_ilmanen

Email: akseli.ilmanen[at]gmail.com

Brain Space Time Podcast, my blog, other stuff

Music: Space News, License: Z62T4V3QWL

Timestamps:

(00:00:00) - Intro

(00:04:52) - Studying language in the real world

(00:07:57) - Wittgenstein

(00:11:10) - Evolution and the default mode network

(00:20:54) - Overparameterized deep learning works

(00:25:02) - Direct Fit paper and generalization

(00:39:37) - Episodic memory and sociality in language models

(00:47:15) - 1000 days project and talking to crows

(00:52:14) - "Understanding" in neuroscience

Kevin Mitchell is an Associate Professor of Genetics and Neuroscience at the Trinity College Dublin. He recently published his second book, "Free Agents: How Evolution Gave Us Free Will." It's a rigorous defense for why we (and other living systems) have free will, arguing all the way from quantum indeterminacy, to C. elegans, to how humans can form abstracted meanings over very long timescales. We also go beyond the book, exploring how free will links to unresolved questions in physics about the discrepancy of microscopic laws being time-invariant and macroscopic laws having a time asymmetry (entropy increase over time). And how the 'present' does it exist and how its duration might differ for a fly vs a human. Kevin also does a great job of explaining why top-down causality and meaning are not just some mythical concepts, but how it scientifically makes sense to speak of neural activity in terms of 'what this means for the orgasm', and how coarse-gaining allows hierarchical control structures to do causal work on this 'meaning-level'. In the end, we also talk about what kind of research Kevin would like to see and advice on learning across disciplines.

For Apple Podcast users, find books/papers links at: https://akseliilmanen.wixsite.com/home/post/pod07

Kevin's Website

Twitter: @WiringTheBrain

Kevin's publications & talks:

Mitchell, 2020 - Innate: How the Wiring of Our Brains Shapes Who We Are book

Potter et al., 2022 - Naturalising Agent Causation paper

Mitchell, 2023 - The origins of meaning – from pragmatic control signals to semantic representations preprint

Mitchell, 2023 - Free Agents: How Evolution Gave Us Free Will book

Mitchell et al., 2023 - Robert Sapolsky vs Kevin Mitchell: The Biology of Free Will | Philosophical Trials #15 YouTube

Mitchell, 2023 - Reflections on “Systems – the Science of Everything” Blog

Other papers/books mentioned:

Smolin et al., 2021 - The quantum mechanics of the present preprint

           
Neuroscience and Philosophy Salon website

My Twitter @akseli_ilmanen

Email: akseli.ilmanen[at]gmail.com

Brain Space Time Podcast, my blog, other stuff

Music: Space News, License: Z62T4V3QWL

Timestamps:

(00:00:00) - Intro

(00:02:40) - The Free Will skeptics

(00:12:56) - Quantum indeterminacy, the weather, and living systems

(00:23:09) - C. elegans and how evolution exploits noise

(00:38:08) - The arrow of time and the quantum mechanics of the present

(00:43:50) - 'How long' is the present for flies vs humans

(00:52:14) - Top-down causality on the biological implementation level

(01:00:03) - Meaning as functional (not epiphenomenal) and Robert Nozick's pleasure machine

(01:05:34) - Interdisciplinary science and education

Kate Jeffery is the head of the school of psychology & neuroscience at the University of Glasgow (formerly at UCL). This episode is all about grid cells (background info), which Kate was already recording in the 1990s. We discuss how grid cells' rate maps differ when the rats climb in 3D spaces. Here we cover anything from cross-species comparisons (bats, birds), to self-organizing dynamics, and symmetry breaking. Kate also shares her (maybe unpopular) thoughts that the hexagonal grid regularity is not functional but a by-product. We also get physics-y by discussing entropy, evolution, complexity and how they link to memory and the arrow of time. At the end there is career advice and some thoughts on climate change.

For Apple Podcast users, find books/papers links at: https://akseliilmanen.wixsite.com/home/post/pod06

Not familiar with place, grid or head direction cells? Here is my 5min primer.

Kate's Website

Kate's publications:

Jeffery et al., 2015 - Neural encoding of large-scale three-dimensional space—properties and constraints paper

Casali et al., 2019 - Altered neural odometry in the vertical dimension paper

Jeffery et al., 2019 - On the Statistical Mechanics of Life: Schrödinger Revisited paper

Jeffery et al., 2020 - Transitions in Brain Evolution: Space, Time and Entropy paper

Grieves et al., 2021 - Irregular distribution of grid cell firing fields in rats exploring a 3D volumetric space paper

Jeffery, 2022 - Symmetries and asymmetries in the neural encoding of 3D space paper

Rae et al., 2022 - Climate crisis and ecological emergency: Why they concern (neuro)scientists, and what we can do paper

Other reading mentioned:

Cheng, 1986 - A purely geometric module in the rat's spatial representation paper

My article on Michel Foucault and climate change deniers

My Twitter @akseli_ilmanen

Email: akseli.ilmanen[at]gmail.com

The Embodied AI Podcast, my blog, other stuff

Music: Space News, License: Z62T4V3QWL

Timestamps:

(00:00:00) - Intro

(00:02:14) - Missing out on a Nobel Prize

(00:11:05) - Place cells & grid cells interactions

(00:15:19) - Grid cells and rats climbing in 3D

(00:27:24) - (Spatial) ecological niches of rats, bats and birds

(00:32:55) - Self-organizing dynamics

(00:35:36) - 'Speed' in navigating physical vs abstract spaces

(00:40:19) - 3D = 2D planes stitched together?

(00:46:22) - Symmetry breaking in

(00:50:20) - 'A purey geometric module' (Cheng, 1986)

(01:01:24) - Why are grid cells grid-like?

(01:05:22) - Kate's (grid cell) secrets

(01:08:18) - Entropy, evolution, and complexity

(01:17:45) - Memory as metastable states

(01:22:07) - Entropy, memory & the arrow of time

(01:25:03) - Career Advice

(01:28:35) - Climate change & sociology

(01:38:07) - New position in Glasgow

Two weeks ago, I visited the Bernstein conference in Berlin. I had lots of fun, particularly at the poster sessions, where I met William, Movitz, and Shervin. I met with each of them later and recorded the following conversations (on bark benches again^^).

William Walker (Gatsby Computational Neuroscience Unit, London) had a poster on 'Representations of State in Hippocampus Derive from a Principle of Conditional Independence'. We discuss how current deep learning struggles with generalization, lacks priors, and could benefit by learning latent conditionally independent representations (similar to place cells).

Movitz Lenninger (KTH Royal Institute of Technology, Stockholm) had a poster on 'Minimal decoding times for various shapes of tuning curves'. He was puzzled why neurons with periodic tuning curves (such as grid cells) are so rare in the brain considering their superior accuracy. He posits there may be a trade-off between accuracy and encoding time.

Shervin Safavi (Max Planck Institute for Biological Cybernetics, Tübingen) had a poster on linking efficient coding and criticality. We introduce those concepts and talk about why noise is a feature, not a bug. Shervin is also starting a new lab at TU Dresden, where he wants to understand the computational machinery of cognitive processes and he is looking for interdisciplinary-minded applicants!

For Apple Podcast users, find books/papers links at: https://akseliilmanen.wixsite.com/home/post/pod05

Not familiar with place, grid and head direction cells? Here is my 5min primer.

William's publications:

Walker et al., 2023 - Unsupervised representation learning with recognition-parametrised probabilistic models preprint

Walker et al., 2023 - Prediction under Latent Subgroup Shifts with High-Dimensional Observations preprint

Movitz's LinkedIn

Movitz's poster from another conference:

Movitz's publications:

Lenninger et al., 2022 - How short decoding times, stimulus dimensionality and spontaneous activity constrain the shape of tuning curves: A speed-accuracy trade-off preprint

Lenninger et al., 2023 - Are single-peaked tuning curves tuned for speed rather than accuracy? paper

Shervin's Website

Twitter: @neuroprinciples

For Shervin's new lab: interest mailing list

Shervin's publications:

Safavi et al., 2022 - Multistability, perceptual value, and internal foraging paper

Safavi et al., 2023 - Signatures of criticality in efficient coding networks preprint

Synchronization of metronomes video

My Twitter @akseli_ilmanen

Email: akseli.ilmanen[at]gmail.com

The Embodied AI Podcast, my blog, other stuff

Music: Space News, License: Z62T4V3QWL

(00:00:00) - Intro

(00:02:53) - William Walker

(00:32:53) - Movitz Lenninger

(00:55:04) - Shervin Safavi