Neuronal representations of semantic information in the human temporal lobe

• Applicant: Professor Dr. Florian Mormann
• Subject Area: Human Cognitive and Systems Neuroscience ; Cognitive, Systems and Behavioural Neurobiology
• Term: since 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 212842712

The question how the brain encodes semantic information like the identity of objects or persons, has sparked the interest of brain researchers for decades. By measuring the activity of single neurons in the human medial temporal lobe, researchers have found neurons that explicitly encode a particular concept. These include cells which respond to very different pictures of a particular person, and even to their written and spoken name. Little is known about the emergence and function of these concept neurons. They are found in brain areas that are necessary for episodic memory formation, they follow the subjective, conscious perception, and they become active after object recognition has already occurred. It has therefore been hypothesized that they might represent the semantic building blocks that are pieced together to form a mnemonic episode. The aim of this proposal is to further investigate these concept neurons and their role in perception and memory.We propose three experiments related to perception, each of which target a different sensory modality, i.e. visual, auditory, and olfactory perception. First we propose an oddball task to identify potential single-unit correlates of the evoked potential P300. By using auditory stimuli, we investigate the activation of concept cells in states of reduced awareness during sleep and anesthesia. By using olfactory stimulation, we will test the existence of odor-modulated cells in the human limbic system.With respect to memory, we propose a working memory paradigm in which an emphasis is placed on the correct sequence of the stimuli to be remembered in order to test whether this sequence is reflected during the stimulus-selective reactivation of concept neurons in the maintenance phase. With regards to long-term memory encoding, we will test – subsequent to completing the analysis of a morning screening session – whether the successful recall of pictures can be predicted from the activity of concept neurons corresponding to the images presented in the morning. Finally, to address memory consolidation, we plan two experiments on targeted memory reactivation, using on the one hand auditory stimulation via the spoken name of a concept and on the other hand olfactory stimulation via an odor paired with the concept during learning, to try and reactivate the concept cells in order to examine whether this might improve learning for these specific stimuli.

• DFG Programme: Research Grants