Temporal-spatial function analysis of the class-IIa1 motion detection cell of the fly Calliphora phaenicia
The physiology of the horizontal motion detection cell class-IIa1 of the fly Calliphora phaenicia was studied by extracellular recording. The receptive field was treated as a multi-input single output system such that Volterra-Wiener functional formalism could be used to describe the input-output re...
| Summary: | The physiology of the horizontal motion detection cell class-IIa1 of the fly Calliphora phaenicia was studied by extracellular recording. The receptive field was treated as a multi-input single output system such that Volterra-Wiener functional formalism could be used to describe the input-output relation. The present work has three objectives: (1) To study the functional of a subunit called the basic motion detection unit. Interpretation of the kernel's features was obtained by comparing it with the results of transient type stimuli. (2) To investigate the organization of the nonlinear spatial interactions in relation to the hexagonal array of visual elements along the horizontal and vertical lines of symmetry. Two sets of experiments were done to find the difference in the organizations of this interaction under light and dark adapted conditions. (3) To investigate the binocular interaction between two class-IIa1 cells each located in different lobes.
The basic motion detection unit could be modeled by two first and second order self kernels, which are associated with their two channels, and a cross kernel. The modeling response of a single channel is dominated by the contribution from the second order self kernels because the receptive field is of on-off type. The cross kernel predicts the multiplication-like directionally selective motion response. Both white noise and transient type stimuli confirmed that an excitatory effect as well as an inhibitory effect exist when stimulus patterns move in the forward direction and backward direction, respectively. The cross kernel model can be thought of as a correlation model which has delay type linear filters (instead of differential and integration type filters). An inhibition model with four types of inhibitory interactions was developed which adequately explained the function of this basic motion detection unit.
Horizontally and vertically aligned eight-stripe white noise patterns were used to investigate the receptive field organization. Under dark adapted conditions the interaction was limited to six adjacent columns and rows. The horizontal cross kernels reveal directionally selective characteristics and have significant 'weights' for those describing the interactions between one column and the nearest four adjacent columns. The vertical cross kernels show a mutually excitatory effect, which could be the evidence of neural pooling of photoreceptors. Under light adapted conditions two major differences appeared. They are: (1) Only two horizontal cross kernels, which describe the interactions between one column and the nearest two columns, have significant 'weights'. The interactions outside this range show reversed directionally selective characteristics. (2) All horizontal and vertical cross kernels have negative diagonal components which indicate a mutually inhibitory effect. This could be a nonlinear sensitivity control mechanism. All the above results were studied with monocular preparation.
The binocular interaction was studied by stimulus patterns located both within the binocular region and outside it. The results confirmed that a mutually inhibitory relationship exists between the class-IIa1 cell and its mirror image in the opposite lobe. |
|---|