Semantic memory and the brain: structure and processes A. Martin & L. L. Chao, 2001

1. Semantic memory and the brain: structure and processesA. Martin & L. L. Chao, 2001 Bart Vanheusden Manon Mulckhuyse

2. Semantic memory • Stored information: structure of semantic representations • Processes: semantic working memory system

3. stored information • Object concepts may be represented as distributed feature networks

4. Features • form • motion • use-associated

5. Networks based on form • Tasks: viewing, naming, matching pictures and answering written questions about object features of animal versus tool stimuli. • Animals: more activation lateral region of the fusiform gyrus • Tools: more activation medial fusiform gyrus.

6. Activation animals versus tools

7. Stored information and perception • Correspondence between patterns of activation for viewing and imagining • Information about object-specfic features may be stored within same neural systems that are active during perception of object form

8. Networks based on motion • Task: viewing pictures and words • tools: more activation in left posterior middle temporal gyrus • animals: more activation in superior temporal sulcus • Anatomic near visual motion processing areas (MT)

9. Animals versus tools

10. Network based on use-associated • Tasks: naming, viewing or action word generation for tools versus animals, houses and faces • Tools: more activation left ventral premotor cortex • stored information or action- planning?

11. Localisations of features in the brain

12. Distributed activity However: activation is not limited to one region and is a complex pattern of peaks and valleys distributed over several cortical regions

13. Representation of unique objects • Categorie: famous faces • activity in anterior middle temporal gyrus and temporal pole • anterior regions of the temporal lobe critical for retrieving information about unique entities

14. Temporal lobe • possibility: temporal lobe object representation system is organised hierarchically, with increasing convergence and intergration of information occuring along its posterior tot anterior axis

15. Hierarchically organisation in temporal lobe

16. processes • Left inferior prefrontal cortex (LIPC) may serve as ‘semantic working memory system’ responsible for retrieving, maintaining, monitoring and manipulating semantic representations stored elsewhere

17. Processes in LIPC • Task: making semantic versus non semantic judgements to words • semantic judgements: more activity in LIPC • Task: repeated performance on semantic versus non semantic tasks • repeated performance semantic tasks: decrease of activation in LIPC

18. processes in LIPC • Task: judging same meaning of sentences determined by synonyms versus syntax • synonyms: more activation LIPC

19. Semantic working memory system • Polar region of left temporal lobe may also contribute to the functioning of semantic working memory system

20. Processes in left temporal cortex • Task: semantic association task normal subjects versus patients with semantic dementia • semantic dementia patients: normal activation in subregions of the left anterior temporal lobe, but no activation in ventral and lateral regions of the posterior left temporal cortex

21. Semantic working memory system • Polar region of the left temporal lobe may provide top-down modularity input necessary for succesful retrieval of semantic representations stored in posterior regions

22. Semantic memory working system

23. Semantic memory: structure and processes • Future research: • precise role of the regions in objects semantics • influence by experience • nonfeature semantic object information and abstract concepts • networks underlying semantic working memory system

24. Questions?