Biology subjects

Kivisaari, S. L.

Publications and source records attributed to Kivisaari, S. L..

3 recordsLinked to original sources

bioRxiv2022

Cortical time-course of evidence accumulation during semantic processing

Our understanding of the surrounding world and communication with other people are tied to mental representations of concepts. In order for the brain to recognize an object, it must determine which concept to access based on information available from sensory inputs. In this study, we combine magnetoencephalography and machine learning to investigate how concepts are represented and accessed in the brain over time. Using brain responses from a silent picture naming task, we track the dynamics of semantic processing, and show that the brain gradually accumulates semantic information before eventually reaching a plateau. The timing of this plateau point varies across individuals, indicating differences in the temporal domain of semantic processing, a new dimension of individual variability in the faculty of language.

neuroscience↗

bioRxiv2019

Serial position effects reflect the integrity of distinct brain regions in Major and Minor Neurocognitive Disorder

Serial Position Effects (SPE) in wordlist learning provide a rich set of metrics of cognitive functioning. In this study, we systematically mapped the neuroanatomical correlates of SPEs across delays in Major and Minor Neurocognitive disorders. Primacy, middle, and recency SPE scores of the California Verbal Learning Test at Learning, Short delay, and Long delay in healthy controls and patients with neurodegenerative disease were correlated with MRI gray matter signal intensities (voxel-based morphometry, VBM). The VBM analyses revealed distinct patterns of brain-behavioral correlations depending on both the SPE and the time-point. Unlike patients, the healthy controls performance incrementally improved recall of primacy items from Learning to Short and to Long delay, i.e., primacy progression. Moreover, the proportion of correct primacy items recalled at long delay compared to Learning correlated with bilateral medial temporal lobe regions, which commonly bear the brunt of pathology of Alzheimers disease. The results implicate the primacy progression score as an accessible and sensitive measure for disease detection, progression, and therapeutic response in Major and Minor Neurocognitive disorders.

neuroscience↗

bioRxiv2018

Reconstructing meaning from bits of information

We can easily identify a dog merely by the sound of barking or an orange by its citrus scent. In this work, we study the neural underpinnings of how the brain combines bits of information into meaningful object representations. Modern theories of semantics posit that the meaning of words can be decomposed into a unique combination of individual semantic features (e.g., \"barks\", \"has citrus scent\"). Here, participants received clues of individual objects in form of three isolated semantic features, given as verbal descriptions. We used machine-learning-based neural decoding to learn a mapping between individual semantic features and BOLD activation patterns. We discovered that the recorded brain patterns were best decoded using a combination of not only the three semantic features that were presented as clues, but a far richer set of semantic features typically linked to the target object. We conclude that our experimental protocol allowed us to observe how fragmented information is combined into a complete semantic representation of an object and suggest neuroanatomical underpinnings for this process.

neuroscience↗