The responses of V1 cortical neurons to flashed presentations of orthogonal single lines and edges

Characterization of receptive fields in the dorsal lateral geniculate nucleus of the tammar wallaby

Orientation selectivity is a prominent feature of neurons in the mammalian primary visual cortex (V1), yet its emergence along the visual pathway varies across species. In carnivores and primates, neurons with elongated and orientation-selective receptive fields (RFs) emerge in V1, whereas in mice such RFs appear earlier, in the retina or dorsal lateral geniculate nucleus (dLGN). Here, we investigate the RF properties of neurons in the dLGN of a marsupial, the wallaby (Macropus eugenii) (n = 2; males), using multichannel electrodes and nonlinear input model (NIM) analysis. Do dLGN RFs resemble those of carnivores and primates or exhibit unique characteristics, particularly regarding orientation selectivity? We found that 82% of neurons have a predominant ON-center response. We identified two main cell types: X-cells (n = 15/22), which exhibit linear properties, and Y-cells (n = 7/22), which display nonlinear characteristics. Most dLGN RFs were blob-like and lacked the oriented structures seen in cortical neurons but some had slightly elongated central areas. These results indicate that robust orientation selectivity develops fully in V1 (76% of neurons). However, mild orientation biases were observed in 41% of dLGN neurons. This study enhances our understanding of visual processing in marsupials and underscores the evolutionary significance of orientation selectivity in mammalian visual pathways.NEW & NOTEWORTHY This study examines receptive field (RF) properties of neurons in the dorsal lateral geniculate nucleus (dLGN) of wallabies using multichannel electrodes and nonlinear input model (NIM) analysis. We identified two main cell types: X-cells (linear) and Y-cells (nonlinear). Most dLGN RFs were blob-like, with mild orientation biases in 41% of neurons, indicating robust orientation selectivity develops fully in primary visual cortex (V1) (76% of neurons).

[Pilot study: Determination of the subjective trunk vertical in upright head position]

BACKGROUND

Consensus has been established that the subjective vertical (SV) is a result of multimodal sensory integration. In order to be able to calculate the vestibulocervical sensory competence for the SV, the isolated subjective trunk vertical axis (STV) was measured under conditions of vertical head fixation.

MATERIALS AND METHODS

Young, healthy volunteers (n = 49) were compared to older, healthy volunteers (n = 50) on a three-dimensionally deflectable (tilt, torsion, pitch) trunk excursion chair in which the volunteer's head remains in an upright position. Another young, healthy group was divided into a placebo (n = 27) and a monophasic cervical transcutaneous electrical nerve stimulation (C-TENS; n = 22) group to examine verticality perception.

RESULTS

In the STV after trunk pitch, age was a significant variable (p = 0.021). The older, healthy group of subjects missed the physical vertical by an average of 1.8° more than the younger group. Only the placebo group showed an average improvement in STV of 4.3° after torsion.

CONCLUSION

Apart from the macular organs the vestibulocervical sensory afference is involved in finding the trunk vertical. A difference in age to the disadvantage of the older healthy subjects was observed, as well as a lack of learning success after applied C‑TENS. The presented pilot study was able to confirm that a correct vertical trunk sensation is caused by vestibulocervical sensory afference in upright head position.