Abstract-1
During discourse comprehension, every new word adds to an evolving representation of meaning that accumulates over consecutive sentences and constrains the next words. To minimize repetition and utterance length, languages use pronouns, like the word ‘she’, to refer to nouns and phrases that were previously introduced. It has been suggested that language comprehension requires that pronouns activate the same neuronal representations as the nouns themselves. Here, we test this hypothesis by recording from individual neurons in the human hippocampus during a reading task. We found that cells that are selective to a particular noun are later reactivated by pronouns that refer to the cells’ preferred noun. These results imply that concept cells contribute to a rapid and dynamic semantic memory network which is recruited during language comprehension. This study uniquely demonstrates, at the single-cell level, how memory and language are linked.
D.E.Dijksterhuis, M.W.Self, J.K.Possel, J.C.Peters, E.C.W.van Straaten, S.Idema, J.C.Baaijen, S.M.A.van der Salm, E.J.Aarnoutse, N.C.E.van Klink, P.van Eijsden, S.Hanslmayr, R.Chelvarajah, F.Roux, L.D.Kolibius, V.Sawlani, D.T.Rollings, S.Dehaene, P.R.Roelfsema. Pronouns reactivate conceptual representations in human hippocampal neurons. Science, 2024-9. [LINK]
Abstract-2
Neural coding has traditionally been examined through changes in firing rates and latencies in response to different stimuli. However, populations of neurons can also exhibit transient bursts of spiking activity, wherein neurons fire in a specific temporal order or sequence. The human brain may utilize these neuronal sequences within population bursts to efficiently represent information, thereby complementing the well-known neural code based on spike rate or latency. Here we examined this possibility by recording the spiking activity of populations of single units in the human anterior temporal lobe as eight participants performed a visual categorization task. We find that population spiking activity organizes into bursts during the task. The temporal order of spiking across the activated units within each burst varies across stimulus categories, creating unique stereotypical sequences for individual categories as well as for individual exemplars within a category. The information conveyed by the temporal order of spiking activity is separable from and complements the information conveyed by the units’ spike rates or latencies following stimulus onset. Collectively, our data provide evidence that the human brain contains a complementary code based on the neuronal sequence within bursts of population spiking to represent information.
Weizhen Xie, John H.Wittig Jr, Julio I.Chapeton, Mostafa El-Kalliny, Samantha N.Jackson, Sara K.Inati & Kareem A.Zaghloul. Neuronal sequences in population bursts encode information in human cortex. Nature, 2024-10. [LINK]
Abstract-3
Olfaction is a fundamental sensory modality that guides animal and human behaviour1,2. However, the underlying neural processes of human olfaction are still poorly understood at the fundamental—that is, the single-neuron—level. Here we report recordings of single-neuron activity in the piriform cortex and medial temporal lobe in awake humans performing an odour rating and identification task. We identified odour-modulated neurons within the piriform cortex, amygdala, entorhinal cortex and hippocampus. In each of these regions, neuronal firing accurately encodes odour identity. Notably, repeated odour presentations reduce response firing rates, demonstrating central repetition suppression and habituation. Different medial temporal lobe regions have distinct roles in odour processing, with amygdala neurons encoding subjective odour valence, and hippocampal neurons predicting behavioural odour identification performance. Whereas piriform neurons preferably encode chemical odour identity, hippocampal activity reflects subjective odour perception. Critically, we identify that piriform cortex neurons reliably encode odour-related images, supporting a multimodal role of the human piriform cortex. We also observe marked cross-modal coding of both odours and images, especially in the amygdala and piriform cortex. Moreover, we identify neurons that respond to semantically coherent odour and image information, demonstrating conceptual coding schemes in olfaction. Our results bridge the long-standing gap between animal models and non-invasive human studies and advance our understanding of odour processing in the human brain by identifying neuronal odour-coding principles, regional functional differences and cross-modal integration.
Marcel S.Kehl, Sina Mackay, Kathrin Ohla, Matthias Schneider, Valeri Borger, Rainer Surges, Marc Spehr & Florian Mormann. Single-neuron representations of odours in the human brain. Nature, 2024-10. [LINK]
Abstract-4
Working memory (WM) and long-term memory (LTM) are often viewed as separate cognitive systems. Little is known about how these systems interact when forming memories. We recorded single neurons in the human medial temporal lobe while patients maintained novel items in WM and completed a subsequent recognition memory test for the same items. In the hippocampus, but not in the amygdala, the level of WM content-selective persistent activity during WM maintenance was predictive of whether the item was later recognized with high confidence or forgotten. By contrast, visually evoked activity in the same cells was not predictive of LTM formation. During LTM retrieval, memory-selective neurons responded more strongly to familiar stimuli for which persistent activity was high while they were maintained in WM. Our study suggests that hippocampal persistent activity of the same cells supports both WM maintenance and LTM encoding, thereby revealing a common single-neuron component of these two memory systems.
Jonathan Daume, Jan Kamiński, Yousef Salimpour, Andrea Gómez Palacio Schjetnan, William S. Anderson, Taufik A. Valiante, Adam N. Mamelak, Ueli Rutishauser. Persistent activity during working memory maintenance predicts long-term memory formation in the human hippocampus. Neuron, 2024-10. [LINK]
Speaker: Xiangyuan Peng
Time: 9:00 am, 2024/10/21
Location: CIBR A622
