Browsing by Subject "V1"

Now showing 1 - 4 of 4

Does locomotion drive V1 activity in primates?
(2022-05-04) Liska, John Paul; Huk, Alexander C.; Colgin, Laura; Cormack, Lawrence; Hayhoe, Mary; Nauhaus, Ian
Our knowledge of the visual input to primary visual cortex (V1) has underpinned the last half century of visual neuroscience. The leaps taken in our ability to understand and interrogate the complex web of interconnected visual areas and their constituent circuits that make up the human visual pathway rest on this understanding of the earliest part of the visual cortex. Although the visual system is a convenient model system because it is relatively easy to present well-controlled inputs to subjects who sit still and keep their eyes steady, real vision occurs as part of a sensorimotor loop that has gone largely ignored within neurophysiological study. Our knowledge of how sensorimotor functions impact visual processing, even at the earliest stages of vision, is nascent and incomplete. These gaps in our understanding extend to even the behavior most core to our survival: our ability to locomote, to move through our environment. Efforts in model systems with visual pathways distinct from those of the primate have made promising insights into just how locomoting may affect the activity of the earliest areas of visual cortex, however, it remains unclear whether these findings generalize to the uniquely evolved primate visual system. In the body of this thesis, I describe and discuss the findings from an effort to discern whether locomotion-induced V1 modulations are present in a primate visual system, that of the common marmoset. I then discuss the challenges encountered in designing and performing these experiments in a recently-adopted model species and present the novel methods developed as a result. I primarily found that strong, population-level locomotion effects like those observed in rodents were not present in primate V1, however a subpopulation of cells does experience small modulations that correlate with locomotion. Additional analyses suggest an explanation based on differential magnitudes of gain fluctuations in mouse versus marmoset V1. The findings reported here indicate that there are fundamental differences in the pathways mediating behavioral input to mammalian V1 across species, presenting a case that cross-species generalizations about visual processing must be considered with greater care in the future.
Exploring mechanisms for contextual modulation in V1
(2022-12-02) Whitmire, Matthew P.; Seidemann, Eyal; Geisler, Wilson S; Huk, Alexander C; Huth, Alexander G; Priebe, Nicholas J; Zemelman, Boris V
The brain can quickly take complex visual information in a scene and group together or distinguish relevant features, allowing us to seamlessly interpret and interact with the world around us. Evidence from recordings in visual cortex have shown that neurons not only responsive to stimuli within their receptive field, but also sensitive to stimuli in the surrounding area. This effect is referred to as contextual modulation. The primary visual cortex (V1) represents high resolution spatial information and stands as the bottleneck before all other visual processing in the cortex, making it a prime location to study complex mechanisms for sensory encoding, like contextual modulation. This dissertation investigates contextual modulation mechanisms present in V1 by: 1) testing if the large-scale population activity in V1 contributes to contour grouping while a monkey is engaged in a complex and difficult contour detection task, and 2) comparing how excitatory and inhibitory cell populations in V1 contribute to orientation tuning, size tuning, and surround modulation effects. First, I will show that we can train rhesus macaques to reliably perform a complex contour detection task with stimuli based on the statistics of contours found in natural scenes. Next, I will demonstrate that when recording voltage sensitive dye imaging signals during the contour detection task, V1 does not show evidence of participating in the contour grouping computation. This suggests V1 may only relay information from individual elements, which are then grouped together in subsequent visual areas. Continuing, I will present that inhibitory cells in macaque V1 show orientation tuning and orientation maps with broader tuning than excitatory cells. Then, I will demonstrate that inhibitory and excitatory size tuning and receptive field sizes do not differ substantially and that V1 surround modulation may be sensitive to general discontinuity, rather than only orientation difference. These results do not support key models of inhibition during size tuning effects and open the field to more work comparing contextual modulation effects across excitatory and inhibitory cells in macaque. Overall, this thesis challenges widely held models of contextual modulation in V1, both for contour grouping and how inhibition shapes surround modulation effects.
Receptive field properties and functional selectivity of CaMKII versus PV cells in mouse V1
(2022-05-09) Coello-Reyes, Gabriela; Goris, Robbe L. T.; Geisler, Wilson S.
Through decades of research, we know neurons in the visual cortex are selectively responsive to visual features, but we still have not completely teased apart how different types of neurons respond to these visual presentations and how the response properties of specific classes of inhibitory and excitatory neurons might vary. If we are to determine how different types of interneurons modulate activity, we need to have a thorough cell-type specific response to visual stimuli. In this study we sought to characterize the receptive field sizes, and functional preference for: orientation, direction, and spatial frequency in PV versus CaMKII cells in layer II/III of the mouse primary visual cortex. Using transgenic lines and in-vivo 2-photon calcium imaging we measured the change in fluorescence intensity of GCaMP6S in PV and CaMKII cells responding to various stimuli. We found that both PV and CaMKII neurons have orientation, direction, and spatial frequency selectivity but the population distribution of these functional properties did significantly differ among the two cell classes. In both direction and orientation selectivity methods we found PV cells to be more selective than CaMKII cells. We also found that the receptive field size distribution significantly differed in PV vs CaMKII cells, with CaMKII Receptive fields being slightly larger than PV receptive fields.
Studies of photoreceptor throughput to visual cortex
(2021-11-04) Rhim, Issac; Nauhaus, Ian; Huk, Alex; Priebe, Nicholas; Seidemann, Eyal
The work in this dissertation aims to (1) examine the presence of a functional map in the mouse visual cortex by measuring its variable cone M-opsin and S-opsin inputs, as predicted by the graded dorsoventral cone opsin expression in the retina (Rhim et al., 2017), (2) devise a method for measuring rod saturation and utilize it to characterize differential spatio-temporal tuning between rod-mediated and cone-mediated vision in V1 (Rhim et al., 2021), and (3) study the representation of color and form. We report that the dorsoventral cone opsin expression gradient in the retina is recapitulated in the mouse visual cortex, including primary visual cortex (V1) and higher visual areas (HVAs). This provides a first finding of a functional map in the mouse cortex, next to retinotopy map. Next, we exploit this feature in the mouse cortex to measure variable opsin inputs to the cortex to provide a model to estimate rod saturation. This is a much-needed foundation in mouse vision research, which will help future studies to differentially quantify inputs from the three photoreceptor opsins found in mice: rhodopsin, S-opsin, and M-opsin. We exemplify this by studying the spatio-temporal tuning of rod-mediated vs. cone-mediated vision in V1. Cone-mediated V1 responds to 2.5-fold higher temporal frequencies than rod-mediated V1, highlighting differences in rod vs. cone information throughput. Lastly, we study the mechanisms underlying spatio-chromatic processing in the cortex. We find that V1's spatial frequency (SF) tuning is more low-pass to color contrast than brightness (i.e., luminance) contrast. Furthermore, our data can be accounted by a random wiring model with rhodopsin and cone S-opsin inputs to single-opponent V1 neurons. While classic models of single-opponency require selective wiring for ON and OFF subfields from each photoreceptor class, we find this to be inconsistent with our data. This provides a new insight to mechanism underlying color vision.