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Many experimental measurements support the hypothesis that the middle temporal visual area (MT) of the rhesus monkey has a central role in processing visual motion. Most of these studies were performed using luminance stimuli, leaving open the question of how color information is used during motion processing. We investigated the specific question of how S-cone signals, an important source of color information, interact with L,M-cone signals, the dominant source of luminance information. In MT, S-cone-initiated signals combine synergistically with L,M-cone (luminance) signals over most of the stimulus range, regardless of whether the stimuli are added or subtracted. A quantitative analysis of the responses to the combination of S- and L,M-cone signals shows that for a significant minority of cells, these S-cone signals are carried to MT by a color-opponent ("blue-yellow") pathway, such that in certain limited contrast ranges, a small amount of S- and L,M-cone cancellation is observed. Both S- and L,M-cone responses are direction-selective, suggesting that MT processes a wide range of motion signals, including those carried by luminance and color. To investigate this possibility further, we measured MT responses while monkeys discriminated the direction of motion of luminance and S-cone-initiated gratings. The sensitivity of single MT neurons and the correlation between trial-to-trial variations in single neuron firing and perception are similar for S- and L,M-cone stimuli, further supporting a role for MT in processing chromatic motion.

Decision-making often involves using sensory cues to predict possible rewarding or punishing reinforcement outcomes before selecting a course of action. Recent work has revealed complexity in how the brain learns to predict rewards and punishments. Analysis of neural signaling during and after learning in the amygdala and orbitofrontal cortex, two brain areas that process appetitive and aversive stimuli, reveals a dynamic relationship between appetitive and aversive circuits. Specifically, the relationship between signaling in appetitive and aversive circuits in these areas shifts as a function of learning. Furthermore, although appetitive and aversive circuits may often drive opposite behaviors – approaching or avoiding reinforcement depending upon its valence – these circuits can also drive similar behaviors, such as enhanced arousal or attention; these processes also may influence choice behavior. These data highlight the formidable challenges ahead in dissecting how appetitive and aversive neural circuits interact to produce a complex and nuanced range of behaviors.

The interaural difference in the level of sounds is an important cue for the localization of the sound's source. In the barn owl, a keen auditory predator, this binaural cue is first computed in the nucleus ventralis lemnisci laterale, pars posterior (VLVp), a cell group found within the fibers of the lateral lemniscus. Its neurons are excited by inputs from the contralateral ear and inhibited by inputs to the ipsilateral ear and are therefore sensitive indicators of interaural level difference. The excitation arrives by a direct input from the contralateral nucleus angularis, a cochlear nucleus, and the inhibition is mediated by a commissural projection that interconnects the VLVps of the two sides. The dorsally located neurons in the VLVp are more heavily inhibited than those found more ventrally, thus giving rise to a gradient of inhibition. This inhibitory gradient plays a central role in recent models of VLVp function. We present evidence based on standard anterograde tracing methods that this gradient of inhibition is mediated by a dorsoventral gradient in the density of synaptic inputs from the contralateral VLVp, the source of inhibition. Specifically, injection of tracers into one VLVp, regardless of the position of the injection within the nucleus, produced a vertically oriented field of label that was densest along the dorsal margin of the contralateral VLVp and became sparser a more ventral levels. Furthermore, we found that injections into the medial and lateral aspects of the nucleus produced this dorsoventrally graded field of label along the medial and lateral aspects of the contralateral VLVp, respectively. Finally, we confirmed an earlier observation suggesting that the anterior and posterior aspects of one VLVp project to the anterior and posterior aspects of the contralateral nucleus, respectively.

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