Cortical hierarchy

Minimising cortical prediction errors is thought to be a key computation underlying perception, action, and learning. Yet, how the cortex represents and uses uncertainty in this process remains unclear. In the first part of this talk, I will present a normative framework showing how uncertainty can modulate prediction error activity to yield uncertainty-modulated prediction errors (UPEs), hypothesised to be represented by layer 2/3 pyramidal neurons. We propose that these UPEs are computed through inhibitory mechanisms involving SST and PV interneurons. A circuit model demonstrates how cortica

Neural activity and behavior in awake animals reflect the interaction between multiple fast processes, such as movements, and slow processes, including arousal, neuromodulation, and learning. A variety of experimental and modeling approaches have successfully tackled single aspects along this spectrum, but a comprehensive multi-scale framework is lacking. To address this challenge, we developed two-photon (2p) mesoscope assays to record neural activity at single-cell resolution from the dorsal and lateral cortex of freely running mice during behavior. We found that whole-brain single-cell dyna

…topographies underlying abstract cortical representations remains equivocal. Experience-driven self-organization provides a complementary mechanism for neural circuit development which instead yields conserved features like orientation tuning, but has also mainly been studied in sensory cortices or artificial neural networks (ANNs). Here we pursue a high level perspective on conservation of topographies and feature spaces throughout the cortex using blood oxygen level d

Visual representations become progressively more abstract along the cortical hierarchy. These abstract representations define notions like objects and shapes but at the cost of spatial specificity. By contrast, low-level regions represent spatially local but simple input features. How do spatially non-specific representations of abstract concepts in high-level areas flexibly modulate the low-level sensory representations in appropriate ways to guide context-driven and goal-directed behaviors across various tasks? We present a biologically motivated and trainable neural network model of dyna

…along the sensory-transmodal cortical axis parallels the cortical hierarchy, while diversity of timescales within each area may reflect functional specialization of individual neurons. However, mechanisms that give rise to the diversity of timescales within and across brain areas remain largely unknown. We leveraged a brain-wide dataset of single-neuron activity to characterize the intrinsic timescales across the whole mouse brain. Timescales varied widely across brain region

Despite the diversity of neural responses, the brain is highly structured both at anatomical and functional levels. Neurons in different brain areas exhibit different response profiles (large-scale anatomical organization), and within brain areas, the neurons can sometimes be grouped together into specialized subpopulations (categorical representations). Organization can also be found at the level of the representational geometry in the activity space, typically in the form of low-dimensional structure (e.g. disentangled abstract representations). However, it is unclear how the geometry in the

The perception of an ambiguous stimulus rely on the activation of multiple cortical areas, operating a sensorimotor transformation along the cortical hierarchy. Furthermore, choice related information is found as upstream as the primary sensory areas, suggesting bi-directional communication at all stages of the cortical hierarchy. How do sensory and choice related activities flow and organize across multiple brain areas? Here, we designed a two-alternative forced-choice task (2AFC) in which mice compared stimulation frequencies applied to two adjacent vibrissae. Using two-photon functional ima

…area they were recorded from in the cortical hierarchy and reflect information encoding dynamics. Using laminar recordings, here we investigate the differences of intrinsic timescales between dorsal premotor (PMd) and primary motor (M1) cortex, and across cortical depth, during a visuomotor delayed reaching task in two macaques. For each neuron, autocorrelograms computed from interspike intervals were fitted with an exponential function to estimate the time decay constant (𝜏) as a meas

…The hierarchy has been observed in brain connectivity and cytoarchitecture, as well as the timescale of spiking activity. However, whether further dynamical features of cortical activity follow a hierarchical organization remains an open question.To address this question, we measured single-neuron statistics from the resting-state activity of macaque neocortex (N=6) from several cortical areas (V1, V4, DP, 7A, M1, PMd, vlPFC). We found some non-systemati

Spontaneous neural dynamics manifest in periodic and aperiodic activity, which are hierarchically organized and intrinsic to different brain areas, in a way thought to mediate information processing of environmental stimuli during wake. Particularly prominent are intrinsic neural timescales, a measure of temporal autocorrelation, which reflect functional significance for cognition, changes in gene expression, and modulations in brain disorders. To date, however, less is known about the regional distribution of neural timescales at the whole-brain level during sleep in humans, where the need fo

…be modified to map faithfully onto the cortical hier

…at multiple stages, including subcortically, and in primary-sensory and higher-order cortical areas. A basic and functionally important feature of multisensory convergence is its topography. For example, in the superior colliculus, visual, auditory, and tactile information converge in register, producing a two-dimensional map that drives saccades. Many studies have demonstrated multimodal convergence elsewhere in the brain, but beyond the superior colliculus, t

…This work revealed a hierarchy of intrinsic timescales, which suggests that along the processing hierarchy, the brain

…only information that permeates the cortical hierarchy can influence sensory perception and decision-making, it is critical that noisy external stimuli are encoded and propagated through different processing stages with minimal signal degradation. Here we hypothesize that stimulus-specific pathways akin to cortical topographic maps may provide the structural scaffold for such signal routing. We investigate whether the featur

Episodic memory performance decreases with advancing age. According to theoretical models, such memory decline might be a consequence of age-related reductions in the ability to form distinct neural representations of our past. In this talk, I want to present our new age-comparative fMRI study investigating age-related neural dedifferentiation across different representational levels. By combining univariate analyses and searchlight pattern similarity analyses, we found that older adults show reduced category selective processing in higher visual areas, less specific item representations in oc