Past events

The study of perceptual decision-making is key to understanding complex cognitive behavior. Two decades of recordings in primate parietal cortex suggest that neurons in the lateral intraparietal (LIP) cortex integrate sensory evidence from upstream neurons (presumably MT) in favor of making a decision. However, the causal role of LIP in decision-making had not been tested directly. In this talk, I will present recent experiments that tested whether area LIP—which exhibits strong decision-related activity—is causally related to perceptual decision-making. In contrast to the generally accepted model, we found that inactivation in area LIP had no measurable impact on decision-making behavior (despite having exerted effects in a control task). This finding suggests that strong decision-related activity does not guarantee a causal role in decision-making. To better understand the MT-LIP circuit we then applied a Generalized Linear Model (GLM) to simultaneously recorded MT and LIP neurons. We found that much of MT & LIP responses may be interpreted in simple sensorimotor terms, as opposed to appealing to nuanced cognitive phenomena. These results shift our understanding of decision-related activity in the primate brain and motivate new approaches to further dissecting the circuit.

The vestibular system detects self-motion and in turn generates reflexes that are crucial for our daily activities, such as stabilizing the visual axis (gaze) and maintaining head and body posture. In addition, the vestibular system provides us with our subjective sense of movement and orientation in space. The loss vestibular function due to aging, injury, or disease produces dizziness, postural imbalance, and an increased risk of falls – all symptoms that profoundly impair quality of life. In this talk, I will describe how the brain processes vestibular information in natural conditions. Notably, our work has established how early stages of processing encode vestibular stimuli and integrate them with extra-vestibular cues – for example proprioceptive and premotor information to ensure accurate perception and behaviour. Our experiments have revealed that while vestibular afferents respond identically to externally-generated and actively-generated self-motion, this is not the case at first central stage of sensory processing. Neurons mediating the vestibulo-spinal reflexes, as well as ascending thalamocortical pathways, are robustly activated during externally-generated motion, however their sensory response are cancelled during actively-generated movements. Our work has further revealed that this cancellation of actively-generated vestibular input occurs only in conditions where the actual sensory signal matches the brain’s internal estimate of the expected sensory consequences of active movement. Moreover, when unexpected vestibular inputs becomes persistent during voluntary motion, a cerebellar-based cancellation mechanism is rapidly updated to re-enable the vital distinction between self-generated and externally-applied stimulation to ensure the maintenance of posture and stable perception. In contrast, vestibular pathways mediating the vestibulo-ocular reflex, employ a different strategy. In this pathway, head velocity is robustly encoded whenever the goal is to stabilize gaze, but when the goal is to voluntarily redirect gaze an efferent copy of the gaze command suppresses the efficacy of this reflex pathway. Taken together, these findings have important implications for understanding the neural basis of perception and action during self-motion.

Neighboring neurons in motor cortex exhibit diverse selectivity during sensation, movement preparation, and movement execution. Neuronal selectivity could emerge from diverse mechanisms, including selective connectivity and nonlinear interactions of synaptic inputs in dendrites. We studied dendritic integration in the anterior motor cortex of mice performing a tactile discrimination task with a delayed response (Guo and Li et al., 2014). We constructed a two-photon microscope that allows rapid (~15 Hz) imaging of up to 300 µm of contiguous dendrite while resolving calcium transients in individual dendritic spines. Two galvanometers and a remote focusing mirror (Botcherby et al., 2008) steer 16 kHz lines (24 µm extent) produced by a resonant mirror arbitrarily in three dimensions. Pyramidal neurons were labeled sparsely with GCaMP6f in transgenic mice. We imaged spine and dendritic calcium transients, as well as somatic calcium transients associated with action potentials. We developed methods to computationally remove the influence of backpropagating action potentials (bAPs), which allowed us to quantify the selectivity of spines and dendritic segments during sensation, movement preparation, and movement execution. Nearby spines and dendritic segments share similar selectivity (length constant of signal correlation, ~30 µm). This clustering was more often seen in distal than in proximal dendrites. Using a measure of local autocorrelation, we also found that this reflects distinct “hotspot” locations on the dendrite where nearby dendrite and spines are co-active in time. Hotspot selectivity was correlated with the behavioral selectivity of somatic spikes, suggesting that these locations may have privileged influence over the output of the cell.

Primates live in environments characterized by continuous, complex cycles of social interactions, where the actions of any group member necessarily influences those of the other members. This raises the question of the extent to which adaptive behavior in social encounters involves specialized mechanisms to represent others’ intentions and affective states. In my talk, I will explore this topic at the behavioral level - asking whether monkeys take into account the welfare of their conspecific when making decisions- and at the brain level - asking what type of information about a social partner is encoded by single neurons in the amygdala and anterior insula. I will try yo argue that these two structures carry neuronal mechanisms for empathy and perspective taking.