Biology subjects

Westerberg, J.

Publications and source records attributed to Westerberg, J..

3 recordsLinked to original sources

bioRxiv2018

Binocular modulation of monocular V1 neurons

In humans and other primates, sensory signals from each eye remain separated until they arrive in the primary visual cortex (V1), but their exact meeting point is unknown. In V1, some neurons are activated by stimulation of only one eye (monocular neurons) while most neurons are driven by stimulation of either eye (binocular neurons). Monocular neurons are most prevalent in the main input layers of V1 while binocular neurons dominate the layers above and below. This observation has given rise to the idea that the two eyes signals remain separate until they converge outside V1s input layers. Here, we show that despite responding to only one eye, monocular neurons in all layers, including the input layers, of V1 discriminate between stimulation of their driving eye alone and stimulation of both eyes. This finding suggests that binocular signals occur at an earlier processing stage than previously appreciated as even so-called monocular neurons across all V1 layers encode what is shown to both eyes.

neuroscience↗

bioRxiv2018

Adaptation of Intracortical Signaling Concurs with Enhanced Encoding Efficiency

Stimulus repetitions improve performance despite decreased brain responses, suggesting that the brain is more efficient when processing familiar stimuli. Previous work demonstrated that stimulus repetition enhances encoding efficiency in primary visual cortex (V1) by increasing synchrony and sharpening the orientation tuning of neurons. Here we show that these adaptive changes are supported by an altered flow of sensory activation across the V1 laminar microcircuit. Using a repeating stimulus sequence, we recorded laminar responses in V1 of two fixating monkeys. We found repetition-related response reductions that were most pronounced outside V1 layers that receive the main retinogeniculate input. This repetition-induced suppression was robust to alternating stimuli between the eyes, in line with the notion that repetition suppression is predominantly of cortical origin. Congruent with earlier reports, we found that V1 adaptation to repeating stimuli is accompanied by sharpened neural tuning as well as increased neural synchrony. Current source density (CSD) analysis, which provides an estimate of net synaptic activation, revealed that the responses to repeated stimuli were most profoundly affected within layers that harbor the bulk of cortico-cortical connections. Together, these results suggest that stimulus repetition induces an altered state of intracortical processing resulting in enhanced encoding efficiency of sensory stimuli.

neuroscience↗

bioRxiv2018

Binocular Integration Manifests as a Transient Spiking Increase Followed by Selective Suppression in Primary Visual Cortex

Research throughout the past decades revealed that neurons in primate primary visual cortex (V1) rapidly integrate the two eyes separate signals into a combined binocular response. The exact mechanisms giving underlying this binocular integration remain elusive. One open question is whether binocular integration occurs at a single stage of sensory processing or in a sequence of computational steps. To address this question, we examined the temporal dynamics of binocular integration across V1s laminar microcircuit of awake behaving monkeys. We find that V1 processes binocular stimuli in a dynamic sequence that comprises at least two distinct phases: A transient phase, lasting 50-150ms from stimulus onset, in which neuronal population responses are significantly enhanced for binocular stimulation compared to monocular stimulation, followed by a sustained phase characterized by widespread suppression in which feature-specific computations emerge. In the sustained phase, incongruent binocular stimulation resulted in response reduction relative to monocular stimulation across the V1 population. By contrast, sustained responses for binocular congruent stimulation were either reduced or enhanced relative to monocular responses depending on the neurons selectivity for one or both eyes (i.e., ocularity). These results suggest that binocular integration in V1 occurs in at least two sequential steps, with an initial additive combination of the two eyes signals followed by the establishment of interocular concordance and discordance.\n\nSignificance StatementOur two eyes provide two separate streams of visual information that are merged in the primary visual cortex (V1). Previous work showed that stimulating both eyes rather than one eye may either increase or decrease activity in V1, depending on the nature of the stimuli. Here we show that V1 binocular responses change over time, with an early phase of general excitation and followed by stimulus-dependent response suppression. These results provide important new insights into the neural machinery that supports the combination of the two eyes perspectives into a single coherent view.

neuroscience↗