Article Critique: Spatial Connectivity Matches Direction Selectivity in Visual Cortex

Article Critique: Spatial Connectivity Matches Direction Selectivity in Visual Cortex
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Article Critique: Spatial Connectivity Matches Direction Selectivity in Visual Cortex
Excitatory and inhibitory links are the primary cause of selective neural responses. The selectivity of the L2/3 neurons in the primary visual region for direction is believed to come from intracortical responses that are choosy in behavior. The selectivity of L2/3 neurons of the primary visual cortex for arrangement and direction has unspecific sources of origin. Co-tuned L4 is thought to be responsible for selectivity while the excitement connections between L2/3 neurons play a key role in amplification. However, there is still uncertainty in whether the tuning of L4 is dominant or plays a complementary role to inputs of L2/3. Inhibition might be essential in direction tuning. However, inhibitory connections can be unreliable. Besides, orientation can also result from spatial offset and inhibition of the L2/3 neurons in the retina.
The authors began by establishing an intracortical presynaptic ensemble of the L2/3 neurons to comprehend their individual selectivity. The use of transgenic mice, CaMK2a-GCaMP6 and GAD2-NLS-mcherry in electroporation of 3-5L23 neurons was essential in establishing visual responses. The injection of the modified rabies virus only target the TVA-positive neuron and push it to its presynaptic neurons which allowed it to express dsRed. The two photon-imaging was used to tabulate the presynaptic ensemble from the postsynaptic neuron. Daily records indicated that presynaptic responses gave positive results for more than 12 days from the day of injection. Presynaptic neurons can either be excitatory or inhibitory depending on the emission of dsRed spectra and mCherry. The signals between dsRed and mCherry were separated using multispectral imaging and spectral unmixing.
At 63±13%, the presynaptic neurons are excitatory with convergence at 70% in high yield experiments. Both excitatory and inhibitory ensembles at L2/3 indicated laminar and horizontal patterns. At L4 excitatory inputs were higher indicated by more extensive vertical and horizontal ranges. On the other hand, the inhibitory response in L2/3 was higher at the postsynaptic neuron. Regardless of layers, the arrangement of postsynaptic neurons matches with an excitatory presynaptic ensemble which matches with earlier observations. In the experiment, most of the postsynaptic and presynaptic neurons responded to the gratings. However, various presynaptic ensembles varied in their arrangement and bearing. In the study, presynaptic neurons chose the postsynaptic preferred arrangement to the orthogonal orientation. The co-tuning was present in both L2/3 and L4 neurons. The spatial patterns in both L2/3 and L4 neurons manifest concerning preferable visual paths.
Angular density in the visual space of excitatory and inhibitory presynaptic neurons in relation with postsynaptic neuron was used to measure the variations in density between excitatory and inhibitory ensembles. In the research, the orthogonal visual sectors that are preferable to direction were more favorable to the excitatory ensemble. The inhibitory e...