Robust effects of corticothalamic feedback and behavioral state on movie responses in mouse dLGN

Neurons in the dorsolateral geniculate nucleus (dLGN) of the thalamus receive a substantial proportion of modulatory inputs from corticothalamic (CT) feedback and brain stem nuclei. Hypothesizing that these modulatory influences might be differentially engaged depending on the visual stimulus and behavioral state, we performed in vivo extracellular recordings from mouse dLGN while optogenetically suppressing CT feedback and monitoring behavioral state by locomotion and pupil dilation. For naturalistic movie clips, we found CT feedback to consistently increase dLGN response gain and promote tonic firing. In contrast, for gratings, CT feedback effects on firing rates were mixed. For both stimulus types, the neural signatures of CT feedback closely resembled those of behavioral state, yet effects of behavioral state on responses to movies persisted even when CT feedback was suppressed. We conclude that CT feedback modulates visual information on its way to cortex in a stimulus-dependent manner, but largely independently of behavioral state

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Mechanisms of attention in visual cortex and the amygdala

Spatial attention enhances perception at specific locations in the visual field, measured behaviorally as improved task performance and faster reaction times. In visual cortex, neurons with receptive fields at attended locations display enhanced responses. This neural modulation is presumed to underlie the associated behavioral benefit, although the mechanisms linking sensory cortical modulation to perceptual enhancement remain unclear. In studies of spatial attention, experimentalists persuade animals to attend to particular locations by associating them with a higher probability or magnitude of reward. Notably, these manipulations alter in tandem both the absolute expectation of reward at a particular location, as well as the expectation of reward relative to other locations in the visual field. We reasoned that independently changing absolute and relative reward expectations could provide insight into the mechanisms of attention. We trained monkeys to discriminate the orientation of two stimuli presented simultaneously in different hemifields while independently varying the reward magnitude associated with correct discrimination at each location. Behavioral measures of attention were controlled by the relative value of each location. By contrast, neurons in visual area V4 were consistently modulated by absolute reward value, exhibiting increased firing rates, increased gamma-band power, and decreased trial-to-trial variability whenever receptive field locations were associated with large rewards. Thus, neural modulation in V4 can be robustly dissociated from the perceptual benefits of spatial attention; performance could be enhanced without neural modulation, and neural activity could be modulated without substantial perceptual improvement. These data challenge the notion that the perceptual benefits of spatial attention rely on increased signal-to-noise in V4. Instead, these benefits likely derive from downstream selection mechanisms. In identifying brain areas involved with attention, a distinction is generally made between sensory areas like V4— where the representation of the visual field is modulated by attentional state— and attentional “source" areas, primarily in the oculomotor system, that determine and control the locus of attention. The amygdala, long recognized for its role in mediating emotional responses, may also play a role in the control of attention. The amygdala sends prominent feedback projections to visual cortex, and recent physiological studies demonstrate that amygdala neurons carry spatial signals sufficient to guide attention. To characterize the role of the amygdala in the control of attention, we recorded neural activity in the amygdala and V4 simultaneously during performance of the orientation discrimination task. In preliminary data analysis, we note two sets of findings. First, consistent with prior work, we found that amygdala neurons combine information about space and value. Rewards both contralateral and ipsilateral to amygdala neurons modulated responses, but contralateral rewards had a larger effect. Therefore, notably distinct from known attentional control sources in the oculomotor system, spatial-reward responses in the amygdala do not reflect the relative value of locations. Second, we found signatures of functional connectivity between the amygdala and V4 during task performance. Reward cue presentation was associated with elevated alpha and beta coherence, and attention to locations contralateral to the amygdala and inside the receptive field of V4 neurons was associated with elevated inter-area gamma coherence. These results suggest that the amygdala may serve a unique role in the control of spatial attention. Together, these experiments contribute towards an understanding of the brain-to-behavior mechanisms linking neural activity in V4 and the amygdala to the dramatic perceptual and behavioral improvement associated with attention

GANEing traction: the broad applicability of NE hotspots to diverse cognitive and arousal phenomena

GANE proposes that local glutamate-norepinephrine interactions enable “winner-take-more” effects in perception and memory under arousal. A diverse range of commentaries addressed both the nature of this ‘hotspot’ feedback mechanism and its implications in a variety of psychological domains, inspiring exciting avenues for future research

Pupillary contagion is independent of the emotional expression of the face

The concept of pupillary contagion refers to the automatic imitation of observed pupil size and reflects shared autonomic arousal. Previous studies linked the experience of sadness to changes in pupil size. Accordingly, Harrison, Singer, Rotshtein, Dolan and Critchley found evidence for pupillary contagion when the observed face expresses sadness, but not for neutral, happy or angry expressions [Social Cognitive and Affective Neuroscience, 1(1), 5–17. (2006)]. However, differences in eye movements might have influenced previous results. Furthermore, the relatively small sample size of the study merits additional replication. In the current study, we modified the previous experimental design (Harrison et al., 2006) by requiring high attention towards the eye region of the face, which minimized differences in eye movements between facial expressions. In doing so, we demonstrate that the degree of pupillary contagion is independent of the observed emotional expression. Instead, pupil size and emotional expression of the model independently contribute to the observer’s pupil size. The role of pupillary contagion for social communication is discussed