Let s Get to Know the Parietal Lobes!

Transcription

1 Let s Get to Know the Parietal Lobes! A brief primer on parietal lobe function (as it relates to memory). By Rebecca Emily Martin 1 Brodmann Areas associated with parietal lobes BA 3, 1, 2, 5 - somatosensory BA 7 - visuo-spatial imagery, selfprocessing BA 23, 29, 31 - Retrosplenial cortex, posterior cingulate BA 39 - reading, visuo-language processing BA 40 - supramarginal gyrus BA 43 - parietal operculum 2

2 The Parietal Lobes can be divided into 6 main regions lateral medial 3 The Parietal Lobes can be divided into 6 main regions dorsal ventral 4

3 The Parietal Lobes can be divided into 6 main regions posterior anterior 5 The Parietal Lobes can be divided into 6 main regions posterior (This presentation focuses on posterior parietal cortex, PPC) 6

4 Terminology 7 Terminology Lateral Posterior Parietal Cortex (PPC) Includes two main regions separated by the intraparietal sulcus (IPS) superior parietal lobule (SPL) inferior parietal lobule (IPL) 8

5 Terminology superior parietal lobule dorsal posterior parietal cortex BA 7 (and sometimes BA 5 the association cortex) the precuneus 9 Terminology inferior parietal lobule ventral posterior parietal cortex BA 39 and BA 40 the angular and supramarginal gyri which also include the temporoparietal junction Wernicke s area 10

6 Other notable areas: Terminology posterior cingulate cortex, BA 23, 31 (PPC) retrosplenial cortex, BA 29 (Rsp, or RSC) parietal operculum (but we won t talk about this part) 11 somatosensory sensory integration reading language comprehension theory of mind self-processing Function of Lateral Regions 12

7 Notable Networks default network frontoparietal control system dual attentional processes hypothesis (Cabeza, 2008) dorsal parietal attention system ventral parietal attention system 13 Default Network Key Regions: Posterior cingulate/retrosplenial Cortex (considered a hub) Inferior parietal lobule Medial Prefrontal Cortex hippocampus lateral temporal cortex Has inverse relationship with cognitive control networks. Associated with autobiographical memory Buckner et al., 2007 Red = default network Blue = cognitive control networks 14

8 Familiarity Dual Attentional Processes Hypothesis of attention to Memory Recollection Dorsal PPC includes SPL and IPS top-down, preparatory, goaldriven allocation of attention Ventral PPC includes IPL and TPJ bottom-up, reflexive reorienting of attention to behaviorally relevant information Cabeza, Nat Rev Neuro 2008 c 7 dorsal attention system (similar to dorsal attn. network) Familiarity Recollection red - familiar blue - remember Low-confidence recognition High-confidence recognition Figure 4 Ventral dorsal dissociations in activity. a In a functional MRI (fmri) study of the remember know paradigm60, the ventral parietal cortex (VPC) showed greater activity for remember than for know trials, whereas the Naturerecognition Reviews Neuroscienc dorsal parietal cortex (DPC) showed the opposite pattern. b In an fmri study of confidence during memory6 the VPC showed greater activity for high- than for low-confidence hits, whereas the DPC showed the opposite pattern. c A meta-analysis of parietal activity during episodic retrieval. The images plot the peaks of activations in two kinds of event-related fmri studies (for a list of studies and coordinates, see Supplementary information S3 (table) and S4 (table)). A first group of peaks (red and dark blue dots) is from studies that identified activity related to recollection or familiarity b using the remember know paradigm, by distinguishing successful from unsuccessful source-memory retrieval, or by comparing the retrieval of items encoded under deep versus shallow study tasks48,49,51,58,59,96, , A second group of peaks (yellow and pale blue dots) is from studies that investigated recognition confidence61,62,81,119. In general, recollection and high-confidence recognition were associated with VPC activations, whereas familiarity and low-confidence recognition were associated with DPC activations. Part a modified, with permission, from REF. 60 (2006) American Physiological Society. Part b modified, with permission, from REF. 63 (2007) Pergamon Press. 15 began as soon as the search instructions were given and continued throughout the search period, whereas VPC activity was greater than DPC activity when the target was detected66. Thus, DPC activity mediates preparatory top-down attention, whereas VPC activity is associated with the capture of bottom-up attention by behaviourally relevant stimuli. Activity that is associated with bottom-up attention can also be captured using unexpected (spatial and non-spatial) stimuli When a relevant stimulus that was out of the current attentional focus appears, the VPC sends a circuit breaker signal to the DPC, which shifts attention to the previously unattended Fronto-parietal Control Network Three key networks: High-confidence recognition stimulus73. The right VPC is also the most frequent loca tion of lesions that cause neglect, which can be describe as a deficit in bottom-up attention: patients with negle can voluntarily direct attention to the contralesional sid and can use cognitive cues to anchor attention to the le visual space, but they have a deficit in detecting stimu that are outside the focus of ongoing processing23. Parietal cortex, attention and episodic memory Could the distribution of episodic-retrieval activation in FIG. 4c be associated with the allocation of top-dow and bottom-up attention to memory by the DPC and th NATURE REVIEWS NEUROSCIENCE VOLUME 9 AUGUST superior parietal lobule, intraparietal lobule, intraparietal sulcus, MT+, ventral premotor cortex and frontal eye fields Hippocampal-cortical memory system (similar to ventral attn. network/ default network declarative memory (e.g. autobiographical) inferior parietal lobule, retrosplenial cortex, posterior cingulate, ventromedial PFC, lateral temporal lobe fronto-parietal control system anatomically interposed between the two systems: anterior PFC, dorsolateral PFC, anterior cingulate, anterior insula, anterior inferior parietal cortex mediates the dorsal attn. and hippocampalcortical memory systems Vincent et al., J. Neurophysiol

9 Memory and the Parietal Lobes Encoding (Uncapher and Wagner, 2009) In a remember/know task: successful remembering was associated with dorsal PPC i.e. the more you pay attention during a task, the more likely you are to remember something forgetting associated with ventral PPC i.e. if you are spacing out your default network is probably more active, and you are less likely to remember Memory and the Parietal Lobes Retrieval (Hutchinson, Uncapher, Wagner, 2009) theories out there but no certainty...more research needed doesn t mirror the dual attention hypothesis main conclusion: attentional mechanisms more involved in encoding than in retrieval Successful remembering associated with ventral regions while less successful remembering associated with dorsal regions dorsal system primarily left-lateralized specialized role for IPS? (visual mapping) ventral system primarily right-lateralized (spatial reorienting) default network also part of the ventral system 18

10 Don t forget the medial parietal regions! Retrosplenial Cortex (Rsp or RSC) considered an intermediate translation zone involved in hippocampal-dependent function (many reciprocal connections with MTL regions) (Vann, Nat Rev Neuro, 2009) Posterior Cingulate Cortex (PCC) considered hub of the default network evaluative region (as opposed to being an executive region like the ACC) (Vogt, Cerebral Cortex, 1992) Precuneus activated during source memory retrieval along with lateral PPC (Cavanna, Brain, 2006) 19 ATN Head direction, theta Parietal cortex Body-oriented information Prefrontal cortex Executive, scene manipulation Egocentric framework Retrosplenial cortex Scene translation Perirhinal cortex Object-based information Hippocampus Event within a scene, scene construction Parahippocampal Scene-based information Allocentric framework Occipital cortex Visual information Figure 3 The key anatomical and functional relationships of the retrosplenial cortex. Effective episodic memory, navigation and future thinking all require the ability to integrate and manipulate different frameworks of information, for example egocentric (self-centred) and allocentric (world-centred) frameworks. By virtue of its principal connections, the retrosplenial cortex is uniquely placed to enable translation within these domains. ATN, anterior thalamic nuclei. 20