Spatio-temporal dynamics of memory in the healthy and brain-damaged subjects
The objective of this research theme is to understand the spatiotemporal dynamics of memory processes, the mechanisms of long-term memory consolidation and the functional relationship of medial temporal components with interconnected structures. We study healthy subjects, patients with epilepsy as well as patients with Alzheimer disease using neuropsychological, electrophysiological and functional MRI methods.Figure 1: Dynamics of ventral stream : feedforward and feedback connections between cortical structures involved in visual memory recognition
Spatiotemporal dynamics of recollection and familiarity.
We study some of the anatomical, neurophysiological and neuropsychological hallmarks of these two processes, both in healthy and brain-damaged subjects (temporal lobe epilepsy as well as Alzheimer’s disease (AD) in its earliest stage). This shall bring further insight into the diagnosis and understanding of the deficits by characterizing functional markers of different neural structures involved in recognition memory.
Mechanisms of long-term consolidation.
We study the mechanisms by which recollection and familiarity processes are involved in the very long-term retrieval of information (i.e., several weeks following successful encoding), whether information involves context-free material or is embedded in a spatio-temporal context. This will be studied in healthy subjects and patients with temporal lobe epilepsy with impaired long-term consolidation using neuropsychological and fMRI.
Functional relationships of Medial Temporal Lobe components with interconnected structures.
In healthy subjects and in subjects at high risk to develop AD, we study the resting-state functional connectivity derived from independent component analysis of low-frequency spontaneous fluctuations of BOLD signal. This study is expected to contribute to the understanding of remote consequences of MTL dysfunction and its components on large-scale network functional connectivity.
Sensorimotor grounding of language and music
The objective of this research theme is to study the emergence of lexical representations (language learning), word recall and song imitation. Another goal is to study the relationship between music and language and see how the comparative study of these uniquely human abilities can shed light on their underlying cognitive and neural mechanisms and on the (beneficial) influence of music on language processing.Figure 2: Interaction between melodic and phonological processing in song
Spatio-temporal brain dynamics underlying the emergence of a rhythmic percept in music and speech
When listening to music it is common to tap along. Tapping the feet or hands means that we are entrained to the musical temporal structure. Our aim is to understand how does this take place in terms of neural dynamics and how this can change in turn the perception of co-occurring or subsequent linguistic stimuli.
Dynamics of the emergence of lexical representations during the learning phase of a new language.
At this aim we study the modulation of the amplitude and latency of ERP components such as the N100 (segmentation) and the N400 (lexicalization), but also of oscillatory activity (ERSP and coherence), possibly signing a perceptual binding phenomenon at word boundaries contributing to the emergence of a “lexical representation.”
Lexical recall mechanisms during word production.
When an epileptic or AD patient is looking for a word or has the word “on the tip of the tongue,” is it a memory problem (retrieval) or is it specific to the object to be recalled (the lexical candidate)? We will try to enhance the understanding of the pathophysiological mechanisms of anomia (ie lack of word) in both populations.
Imitative vocal processes.
We have recently shown that human vocal stimuli are easier to reproduce compared to synthetic stimuli, possibly reflecting a more direct access to motor representation that may allow a preparation of the imitative action. We will test the hypothesis that the connectivity of the audio-motor system can be influenced by the level of imitability and the more or less anthropomorphic character of the sounds perceived.
Cochlear implanted congenitally deaf children.
We have just started to study the dynamics of information transfer from auditory to language capacities in profoundly deaf children undergoing cochlear implant treatment and rehabilitation. Using a longitudinal approach we plan to investigate the emergence and development of the isomorphism between brainstem responses and auditory input in cochlear implanted children, also studying its correlation with speech behavior (e.g. comprehension, fluency, articulation). On a more clinical and integrated ground we will study whether domain-general principles apply to meter and rhythm in language and music processing. We will explore this possibility in the music domain to draw a direct comparison between music and language perception, and extend this approach to speech production with cochlear implanted children and adults.Figure 3: Tracking the evolution of brainstem responses to linguistic sounds
Semiology of epileptic seizures: physiological and phenomenological approaches
- Is a categorization of ictal semiology able to define anatomical patterns of frontal and parietal seizures (origin and propagation), or else to characterize systemic activations of interconnected structures?
- What are the physiological/pathophysiological conditions underlying the ictal expression of elements of cognition/behavior that are within the usual human repertoire, versus “nonsense” elements (frequency bandwidth, local vs remote activation, functional connectivity)?
- Are the ictal automatic behaviors resulting from local cortical activation in the “natural” range of stimulation parameters, or from liberation of basal ganglia, diencephalic, and brain stem activities from cortical control ?
From Intention to action: cognitive integration within the cortical sensorimotors networks
The objectives of this research theme is to understand the activation dynamics of cortical sensorimotor networks allowing an intention to make an action emerge, and how the functional organization of primary and nonprimary area evolves when interactions with cognitive functions increase.
- within the cortical sensorimotor networks, how nonprimary motor area –SMA, PM- interact with the primary sensorimotor area
- the dynamic interactions between cortical sensorimotor networks and prefrontal inhibitory circuits.
Perturbing the dynamic state of the brain allows us to understand its dynamics from the way it reacts to this perturbation. We will use a Perturbing (by stimulation)-Recording approach based on stereotactic TMS combined with EEG.
Figure 4: Stereotactic TMS (based on sophisticated imaging guidance) combined with EEG. It allows an interactive guidance of stimulation into a selected spot of the brain with full real-time visualization of the stimulating electromagnetic fields.