Henley, T. M. | bioRxiv Science

bioRxiv2026

Increased activity without changes in coupling between somata and apical dendrites during visual mismatches

Leading theories of cortical function posit that sensory processing involves a comparison between top-down predictions and bottom-up sensory data. Tests of these theories have been hampered by experimental challenges related to simultaneously recording top-down and bottom-up signals in response to sensory stimuli that either do or do not match internally-generated predictions. Here, we conduct dual-plane 2-photon calcium imaging near-simultaneously from distal apical dendrites and somata of pyramidal neurons in each of 4 different regions of mouse visual cortex while the mice are presented with visual sequences that can either match or mismatch previously habituated visual stimuli. Specifically, we examine the responses in the distal apical dendrites and cell bodies of pyramidal neurons while mice view either movie clips that reverse unexpectedly or Gabor patch sequences that have orientations that do not match habituated patterns. We find that in response to unexpected reversals in natural movies, both the apical dendrites and somata show increased activity that decreases over repeated exposures, consistent with a prediction error response. However, we do not find any clear evidence for increased activity in response to mismatches in Gabor sequences, beyond possible release from adaptation effects. We additionally use volumetric images to connect dendritic and somatic compartments and examine the coupling between connected dendrites and cell bodies in layer 5 pyramidal neurons. We do not find evidence for changes in coupling in response to mismatch stimuli, either for natural movies or Gabor sequences. Our results are consistent across four regions of visual cortex. We also observe that increased responses to reversals in natural movies are stronger in layer 2/3 than layer 5 pyramidal neurons. Altogether, these data suggest that visual cortex is sensitive to deviations from previously-experienced naturalistic inputs. Our data do not suggest that this mismatch sensitivity extends to artificial stimuli, nor do they support theories of prediction error causing changes in the coupling between apical dendrites and somata.

neuroscience↗

bioRxiv2021

Learning from unexpected events in the neocortical microcircuit

Scientists have long conjectured that the neocortex learns the structure of the environment in a predictive, hierarchical manner. According to this conjecture, expected, predictable features are differentiated from unexpected ones by comparing bottom-up and top-down streams of information. It is theorized that the neocortex then changes the representation of incoming stimuli, guided by differences in the responses to expected and unexpected events. In line with this conjecture, different responses to expected and unexpected sensory features have been observed in spiking and somatic calcium events. However, it remains unknown whether these unexpected event signals occur in the distal apical dendrites where many top-down signals are received, and whether these signals govern subsequent changes in the brains stimulus representations. Here, we show that both somata and distal apical dendrites of cortical pyramidal neurons exhibit distinct unexpected event signals that systematically change over days. These findings were obtained by tracking the responses of individual somata and dendritic branches of layer 2/3 and layer 5 pyramidal neurons over multiple days in primary visual cortex of awake, behaving mice using two-photon calcium imaging. Many neurons in both layers 2/3 and 5 showed large differences between their responses to expected and unexpected events. Interestingly, these responses evolved in opposite directions in the somata and distal apical dendrites. These differences between the somata and distal apical dendrites may be important for hierarchical computation, given that these two compartments tend to receive bottom-up and top-down information, respectively.

neuroscience↗