Past events

In this talk I will describe a recent controversy that has arisen regarding the intrinsic properties of Purkinje cells and explain the importance of this controversy to our understanding of Cerebellar function. In brief, it has been shown that Purkinje cell membrane potential is bistable, but there remains significant disagreement about whether this bistability has a functional role. In our lab, we addressed the controversy by recording from Purkinje cells in an awake animal and testing to see whether bistability that had been observed in vitro and in anaesthetized animals could also be seen in a behaving animal. Our findings will not settle the controversy, nor settle the question of the Cerebellum's functional role, but they will significantly shift the terms of the debate. We found that all of the predictions we tested confirmed the potential for a functional role for Purkinje cell bistability. This will force a serious re-evaluation of our understanding of Cerebellar circuitry.

Understanding the functional neuro-anatomy of face processing in the human brain is a long-standing goal of Cognitive Neuroscience. Up to the early 90’s, the most important source of knowledge was from lesion studies, i.e. making correlations between the localization of lesions in groups of brain-damaged patients and their face recognition impairments. The influence of the cognitive approach in Neuropsychology, with an emphasis on single-case functional investigations, as well as the advent of neuroimaging studies in the healthy brain, have considerably reduced the importance of lesion studies in clarifying the neuro-anatomical aspects of face processing. In this talk, my goal will be to illustrate how neuroimaging investigations of single-cases of acquired prosopagnosic patients can still greatly increase our knowledge in this field. Neuroimaging studies of the normal brain have shown that the middle fusiform gyrus (‘FFA’) and the inferior occipital gyrus (‘OFA’) are activated by both detection and identification of faces. Among other observations, our studies of the patient PS, a case of prosopagnosia with normal object recognition, show that the right ‘FFA’ can be recruited to detect faces independently of the ‘OFA’ of the same hemisphere (Rossion et al., 2003). However, fMRI-adaptation investigations suggest that both areas are necessary to perform individual discrimination of faces (Schiltz et al., 2006). Recent observations also show that the the same brain area, here the right ‘FFA’, may be impaired at individual face discrimination while performing normal individual object discrimination. This suggests that clusters of neurons coding specifically for different categories in this area (Grill-Spector et al., 2006) can be functionnally independent. Finally, when structurally intact, non-face preferring areas such as the ventral part of the lateral occipital complex (vLOC) may subtend residual individual discrimination of faces following prosopagnosia. Altogether, these studies show that faces are processed through multiple pathways in the human brain, with a subset of these areas responding preferentially to faces being critical for efficient face recognition.

Unlike the situation in neurophysiology, where the relevant variables are mostly known, it is not clear what is to be measured in the study of behavior; what is a reliable datum? What are the elementary patterns? To highlight the building blocks of movement and their organization we use 4 tools: (i) we study gradients: along the body dimension, in space and in time (in moment-to-moment behavior, ontogeny, and recovery). Gradients provide natural origins of axes for measurement, reveal how building blocks are gradually added on top of each other to form the animal's full repertoire, and unite seemingly disparate behaviors into continua. (ii) We systematically change coordinate systems, to find the ones highlighting invariant features. We use multiple kinematic variables to describe the behavior. They may or may not cluster into discrete patterns. (iii) We study behavior on more than one scale. For example, along the body dimension we use 2 scales that of the path, and that of multi-limb coordination. Finally, (iv) we segment movement using intrinsic geometrical and statistical properties. By using combinations and conjunctions of the elementary building blocks we work our way up from low level to cognition- and motivation-related constructs. In my talk I will describe how these tools are implemented in a bottom-up study of mouse (Mus musculus) and fly (Drosophila melanogaster) exploratory behavior.