Proteoglycan Clusters as a Site of Coordinated, Multi-Dendritic Plasticity

Experience-dependent learning depends on synaptic plasticity. While plasticity in individual synapses has been extensively investigated, the mechanisms underlying coordinated changes across sets of synapses on multiple dendrites, likely needed to encode effective adaptations to a salient stimulus, are not well understood. The extracellular matrix is uniquely well suited to fulfill this function, as rapid glia-driven remodeling of its local composition powerfully impact synaptic plasticity. We show that extracellular matrix microenvironments, named CS6 clusters, dynamically form around several dendrites in response to sensory stimuli in coincidence to stimulus-driven synaptic plasticity. CS6 clusters, formed by glia-dependent secretion of extracellular matrix components surrounding sets of adjacent dendrites, may represent a novel structure supporting coordinated synaptic plasticity.

Oculomotor freezing tracks perception and is immune to decision bias

The appearance of a salient stimulus rapidly inhibits saccadic eye movements. Curiously, this "oculomotor freezing" reflex is triggered only by stimuli that the participant reports seeing (White & Rolfs, 2016). But is oculomotor freezing linked to the participant's sensory experience, or their decision that a stimulus was present? If it were decision-related, oculomotor freezing should become less prevalent when the participant is induced to have a conservative decision criterion and reports seeing a stimulus less often. Here we manipulated decision criterion in two ways: by adjusting monetary payoffs and stimulus probability in a detection task. These bias manipulations greatly affected participants' explicit reports but did not affect the degree to which microsaccades were inhibited by stimulus presence. In addition, the link between oculomotor freezing and explicit reports was stronger when the decision criterion was conservative rather than liberal. The simplest explanation is that conservative reports of stimulus presence are more often based on a strong sensory signal that also inhibits microsaccades. We conclude that the sensory threshold for oculomotor freezing is independent of decision bias. To the extent that conscious experience is also unaffected by such bias, oculomotor freezing provides an involuntary, implicit indication that a stimulus has entered awareness.

Coordination of Pupil and Saccade Responses by the Superior Colliculus

The appearance of a salient stimulus evokes saccadic eye movements and pupil dilation as part of the orienting response. Although the role of the superior colliculus (SC) in saccade and pupil dilation has been established separately, whether and how these responses are coordinated remains unknown. The SC also receives global luminance signals from the retina, but whether global luminance modulates saccade and pupil responses coordinated by the SC remains unknown. Here, we used microstimulation to causally determine how the SC coordinates saccade and pupil responses and whether global luminance modulates these responses by varying stimulation frequency and global luminance in male monkeys. Stimulation frequency modulated saccade and pupil responses, with trial-by-trial correlations between the two responses. Global luminance only modulated pupil, but not saccade, responses. Our results demonstrate an integrated role of the SC on coordinating saccade and pupil responses, characterizing luminance independent modulation in the SC, together elucidating the differentiated pathways underlying this behavior.

The Ant Who Cried Wolf? Short-Term Repeated Exposure to Alarm Pheromone Reduces Behavioral Response in Argentine Ants

In this study we test whether Argentine ants (Linepithema humile) progressively reduce their response to a salient stimulus (alarm pheromone) with increased exposure over time. First, we used a two-chamber olfactometer to demonstrate three focal behaviors of Argentine ants that indicate an alarmed state in response to conspecific alarm pheromone and pure synthetic iridomyrmecin (a dominant component of L. humile alarm pheromone). We then measured how these behaviors changed after repeated exposure to conspecific alarm pheromone from live ants. In addition, we investigate whether there is a difference in the ants’ behavioral response after “short” (3 min) versus “long” (6 min) intervals between treatments. Our results show that Argentine ants do exhibit reduced responses to their own alarm pheromone, temporarily ceasing their response to it after four or five exposures, and this pattern holds whether exposure is repeated after “short” or “long” intervals. We suggest alarm pheromones may be perceived as false alarms unless threatening stimuli warrant a continued state of alarm. These results should be kept in mind while developing pheromone-based integrated pest management strategies.

Increase in internetwork functional connectivity in the human brain with attention capture

The selective properties of attention have been extensively studied. There are some circumstances in which attention can have widespread and systemic effects, however, such as when it is captured by an unexpected, salient stimulus or event. How are such effects propagated in the human brain? Using graph theory analysis of fMRI data, we show here that salient task-irrelevant events produced a global increase in the functional integration of the brain’s neural networks.

Complex spike firing adapts to saliency of inputs and engages readiness to act

The cerebellum is involved in cognition next to motor coordination. During complex tasks, climbing fiber input to the cerebellum can deliver seemingly opposite signals, covering both motor and non-motor functions. To elucidate this ambiguity, we hypothesized that climbing fiber activity represents the saliency of inputs leading to action-readiness. We addressed this hypothesis by recording Purkinje cell activity in lateral cerebellum of awake mice learning go/no-go decisions based on entrained saliency of different sensory stimuli. As training progressed, the timing of climbing fiber signals switched in a coordinated fashion with that of Purkinje cell simple spikes towards the moment of occurrence of the salient stimulus that required action. Trial-by-trial analysis indicated that emerging climbing fiber activity is not linked to individual motor responses or rewards per se, but rather reflects the saliency of a particular sensory stimulus that engages a general readiness to act, bridging the non-motor with the motor functions.In briefMice were trained to identify the saliency of different sensory inputs in that they had to learn to ignore a prominent sound cue and respond to a light tactile cue in a Go/No-Go licking task. As the mice learned to discriminate the two inputs and respond to the proper signal, the Purkinje cells in the lateral cerebellum switched their climbing fiber activity (i.e., complex spike activity) towards the moment of occurrence of the salient stimulus that required a response, while concomitantly shifting the phase of their simple spike modulation. Trial-by-trial analysis indicates that the emerging climbing fiber activity is not linked to the occurrence of the motor response or reward per se, but rather reflects the saliency of a particular sensory stimulus engaging a general readiness to act.

Reaching movements are attracted by stimuli that signal reward

When presented with a set of possible reach targets, the movement trajectory can reveal aspects of the underlying competition for action selection. Current goals and physical salience can affect the trajectory of reaching movements to be attracted towards a distractor. Some studies demonstrated that stimuli associated with reward can also cause an attraction when reaching towards the reward stimulus was previously rewarded and the reward stimulus was physically salient. Here we demonstrate that a non-salient stimulus that signals the availability of reward attracts reaching movements even when moving towards it was never necessary nor rewarded. Moreover, the attraction by reward is particularly evident with short-latency movements. We conclude that neither physical salience nor reinforcing the movement towards a stimulus is necessary for reward to gain priority in the selection for action.

Coordination of pupil and saccade responses by the superior colliculus

The appearance of a salient stimulus evokes saccadic eye movements and pupil dilation as part of the orienting response. Although the role of the superior colliculus (SC) in saccade and pupil dilation has been established separately, whether and how these responses are coordinated remains unknown. The SC also receives global luminance signals from the retina, but whether global luminance modulates saccade and pupil responses coordinated by the SC remains unknown. Here, we used microstimulation to causally determine how the SC coordinates saccade and pupil responses, and whether global luminance modulates these responses by varying stimulation frequency and global luminance in male monkeys. Stimulation frequency modulated saccade and pupil responses, with trial-by-trial correlations between the two responses. Global luminance only modulated pupil, but not, saccade responses. Our results demonstrate an integrated role of the SC on coordinating saccade and pupil responses, characterizing luminance independent modulation in the SC, together elucidating the differentiated pathways underlying this behavior.

Guessing right: Preconscious processing in inattentional blindness

Much research has been conducted on the determinants of inattentional blindness—the failure to miss an unexpected but salient stimulus in plain view. Far less research has been concerned with the fate of those objects that go unnoticed in such a setting. The available evidence suggests that objects that are not consciously noticed due to inattentional blindness are still processed to a certain degree. The present study substantiated and generalised this limited evidence by reanalysing 16 datasets in regard to participants’ guessing accuracy in multiple-choice questions concerning the unexpected object: Participants who did not notice the critical object showed guessing accuracy that lay significantly above chance. Thus, stimuli that are not consciously noticed (i.e., cannot be reported) can nevertheless exert an influence on seemingly random choices. Modality of the primary task as well as performance in the primary task and in a divided-attention trial were evaluated as potential moderators. Methodological limitations such as the design and implementation of the multiple-choice questions and the generalisability of our findings are discussed, and promises of the present approach for future studies are presented.

Visual search mimics configural processing in associative learning

Theories of generalization distinguish between elemental and configural stimulus processing, depending on whether stimuli in a compound are processed independently or as distinct entities. Evidence for elemental processing comes from findings of summation in animals, where a compound of two stimuli that independently predict an outcome is deemed to be more predictive of the outcome than each stimulus alone. Configural processing, on the other hand, is supported by experiments that fail to find this effect when the compound is comprised of similar stimuli. In humans, by contrast, summation seems to be robust and independent of similarity. We show how these results are best explained by an alternative view in which generalization comes about from a visual search process in which subjects process the most predictive or salient stimulus in a compound. We offer empirical support for this theory in three human experiments on causal learning and formalize a new elemental visual search model based on reinforcement learning principles which can capture the present and previous data on generalization, bridging two different research areas in psychology into a unitary framework.