Competitive Disinhibition Mediates Behavioral Choice and Sequences in Drosophila.

Visual scenes comprise enormous amounts of information from which nervous systems extract behaviorally relevant cues. In most model systems, little is known about the transformation of visual information as it occurs along visual pathways. We examined how visual information is transformed physiologically as it is communicated from the eye to higher-order brain centers using bumblebees, which are known for their visual capabilities. We recorded intracellularly in vivo from 30 neurons in the central bumblebee brain (the lateral protocerebrum) and compared these neurons to 132 neurons from more distal areas along the visual pathway, namely the medulla and the lobula. In these three brain regions (medulla, lobula, and central brain), we examined correlations between the neurons' branching patterns and their responses primarily to color, but also to motion stimuli. Visual neurons projecting to the anterior central brain were generally color sensitive, while neurons projecting to the posterior central brain were predominantly motion sensitive. The temporal response properties differed significantly between these areas, with an increase in spike time precision across trials and a decrease in average reliable spiking as visual information processing progressed from the periphery to the central brain. These data suggest that neurons along the visual pathway to the central brain not only are segregated with regard to the physical features of the stimuli (e.g., color and motion), but also differ in the way they encode stimuli, possibly to allow for efficient parallel processing to occur.

https://www.jneurosci.org/content/jneuro/29/32/9987.full.pdf

Visual processing in the central bee brain

In Cupiennius salei (Ctenidae), as in other spiders, the central nervous system is divided into the supraoesophageal ganglion or brain and the suboesophageal ganglia (Fig. 1). The two masses are interconnected by oesophageal connectives. The brain gives off four pairs of optic and one pair of cheliceral nerves. From the suboesophageal ganglia arise a pair of pedipalpal, four pairs of leg, and several pairs of opisthosomal nerves (Fig. 2).

Neuroanatomy of the central nervous system of the wandering spider, Cupiennius salei (Arachnida, Araneida)

In addition to multifaceted lateral compound eyes, most insects possess three frontal eyes called ocelli. Each ocellus has a single lens, as does the vertebrate eye. The ocelli of some flying insects, locusts and dragonflies, have been shown to function as horizon detectors involved in the visual stabilization of course. In a walking insect, the desert ant Cataglyphis, it is now shown that the ocelli can read compass information from the blue sky. When the ant's compound eyes are occluded and both sun and landmarks are obscured, the ocelli, using the pattern of polarized light in the sky as a compass cue, help in guiding the ant back home.

https://science.sciencemag.org/content/sci/228/4696/192.full.pdf

Oceili: A Celestial Compass in the Desert Ant Cataglyphis

The mechanisms of processing a visual scene involve segregating features (such as color) into separate information channels at different stages within the brain, processing these features, and then integrating this information at higher levels in the brain. To examine how this process takes place in the insect brain, we focused on the medulla, an area within the optic lobe through which all of the visual information from the retina must pass before it proceeds to central brain areas. We used histological and immunocytochemical techniques to examine the bumblebee medulla and found that the medulla is divided into eight layers. We then recorded and morphologically identified 27 neurons with processes in the medulla. During our recordings we presented color cues to determine whether response types correlated with locations of the neural branching patterns of the filled neurons among the medulla layers. Neurons in the outer medulla layers had less complex color responses compared to neurons in the inner medulla layers and there were differences in the temporal dynamics of the responses among the layers. Progressing from the outer to the inner medulla, neurons in the different layers appear to process increasingly complex aspects of the natural visual scene.

/pdf/color-processing-in-the-medulla-of-the-bumblebee-apidae-4foalbkvm9.pdf

Color processing in the medulla of the bumblebee (Apidae: Bombus impatiens)

The response characteristics to light stimuli of first order ocellar interneurons in the bee (Apis mellifera carnica) were analysed with intracellular recordings. The neurons were identified using intracellular dye injection (Lucifer yellow). The responses of L-(large) neurons can vary. They range from transient graded hyperpolarizations in response to light-On and -Off, (sometimes accompanied by tonic hyperpolarization during the light stimulus), to spontaneous tonic action potentials which are inhibited by light. Some neurons show both hyperpolarizations and action potentials. The varying responses to light stimuli are dependent only on the state of the L-neuron and are not correlated systematically with particular types of L-neurons. The experiments demonstrate that the action potentials are generated within the L-neurons and are not conducted antidromically from other neurons. The amplitude and frequency of the action potentials depend on the membrane potential of the L-neuron. With light stimulation, or application of hyperpolarizing current, spikes can be generated within some of the L-neurons. Presumably non-spiking L-neurons are refractory due to maintained depolarization. They have membrane potentials of about −40 mV. Action potentials in L-neurons were recorded only with high resistance microelectrodes. The vitality of the animal can not be correlated with the occurrence of spikes. Functional significance of spontaneous tonic spike discharges in L-neurons is discussed in the context of behavioural experiments in the bee. It is possible, that a given L-neuron uses either spiking or non-spiking signal transmission depending on the behavioural situation. Although very fine microcapillary electrodes were used, no successful recordings or stainings of S-(small) neurons in the ocellar nerve were achieved. Therefore, results of non-identified ocellar interneurons which have been attributed to S-neurons should be critically reviewed.

Jfirgen Milde

Papers

Graded potentials and action potentials in the large ocellar interneurons of the bee