Qué PASA? The Posterior-Anterior Shift in Aging Simon W. Davis, Nancy A. Dennis, Sander M. Daselaar, Mathias S. Fleck, & Roberto Cabeza Cerebral Cortex, doi: /cercor/bhm155

Background PASA (posterior-anterior shift in aging): PASA (posterior-anterior shift in aging): 1. an age-related reduction in occipital activity coupled with increased frontal activity (Grady, 1994) 2. PASA pattern has found in attention, visual perception, visuospatial processing, working memory, episodic memory encoding & retrieval

Unfinished issues of PASA Validity of PASA: Validity of PASA: It may simply reflect difference in task difficulty (ic. objective & subject measures of difficulty), especially in its prefrontal cortex (PFC) component. It may simply reflect difference in task difficulty (ic. objective & subject measures of difficulty), especially in its prefrontal cortex (PFC) component. Function of PASA: Function of PASA: No study has found PFC activations in older adults positively associated with performance and negatively associated with occipital activation No study has found PFC activations in older adults positively associated with performance and negatively associated with occipital activation

Unfinished issues of PASA ─ Cont. Generalizability of PASA: Generalizability of PASA: PASA effect has been observed for activation, but not for deactivation PASA effect has been observed for activation, but not for deactivation  Past findings showed attenuated deactivations in posterior midline cortex in healthy older adults. possibility: compensating this deficit by deactivating anterior midline regions to a greater extent than younger adults? possibility: compensating this deficit by deactivating anterior midline regions to a greater extent than younger adults?

Back to the current study 3 predictions: 3 predictions: 1. PASA will exist even eliminating differences in difficulty (the validity of PASA) 1. PASA will exist even eliminating differences in difficulty (the validity of PASA) 2. PFC activity will be positively correlated with cognitive performance and negatively correlated with occipital activity, supporting the compensation account (the function of PASA) 2. PFC activity will be positively correlated with cognitive performance and negatively correlated with occipital activity, supporting the compensation account (the function of PASA) 3. Older adults would show weaker deactivations in posterior midline regions but stronger deactivations in anterior medial regions (the generalizability of PASA) 3. Older adults would show weaker deactivations in posterior midline regions but stronger deactivations in anterior medial regions (the generalizability of PASA)

Methods Participants: 12 younger & 12 older adults were matched by a rank order based on corrected scores of ER and VP performance Participants: 12 younger & 12 older adults were matched by a rank order based on corrected scores of ER and VP performance

Methods-cont. Stimuli Stimuli For the episodic retrieval (ER) task: For the episodic retrieval (ER) task: 240 five-letter words & 80 five-letter pseudowords 240 five-letter words & 80 five-letter pseudowords For the visual perception (VP) task For the visual perception (VP) task 120 rectangles were divided by a jagged line to 2 areas, making different versions of a perceptual stimuli with different difficulty of subject performance 120 rectangles were divided by a jagged line to 2 areas, making different versions of a perceptual stimuli with different difficulty of subject performance

Methods-cont. Behavioral paradigm Behavioral paradigm Prior to scanning * Showing intermixed real words and pseudowords During scanning * 4 runs of the ER & 2 runs of the VP task were performed * accuracy & confidence were rated

Methods-cont. MRI scanning MRI scanning * 4-T GE scanner was used. * The anatomical MRI was acquired using a 3D T1- weighted echo-planar sequence. fMRI analyses fMRI analyses * Event-related blood oxygen level-dependent responses for each participant were analyzed using a modified general linear model

Results Behavioral data Behavioral data

Results-cont. Neuroimaging results Neuroimaging results

Results-cont. Neuroimaging results show PASA was found when differences in task difficulty were eliminated Neuroimaging results show PASA was found when differences in task difficulty were eliminated

Results-cont. Neuroimaging results show in older adults PFC activity was negatively correlated with activity in the occipital cortex, but positively correlated with ER/VP performance; in younger adults, no significant correlations between regions or between activity and performance Neuroimaging results show in older adults PFC activity was negatively correlated with activity in the occipital cortex, but positively correlated with ER/VP performance; in younger adults, no significant correlations between regions or between activity and performance

Results-cont. Neuroimaging results indicated PASA was also found for deactivation Neuroimaging results indicated PASA was also found for deactivation

Discussion Validity of PASA: against a difficulty account Validity of PASA: against a difficulty account After removing difficulty difference, a clear PASA pattern was found─ After removing difficulty difference, a clear PASA pattern was found─ * occipital activity: in younger > in older adults * PFC activity: in older > in younger adults

Discussion-cont. Function of PASA: for the compensation account Function of PASA: for the compensation account * PFC activity compensates for the decrease in occipital activity that is necessary for successful task performance

Discussion-cont. Generalizability of PASA: posterior-anterior shift in deactivations Generalizability of PASA: posterior-anterior shift in deactivations * “Default network”─ previous studies indicated * “Default network”─ previous studies indicated 1. posterior and anterior midline cortices are often deactivated during task compared with a resting baseline. 1. posterior and anterior midline cortices are often deactivated during task compared with a resting baseline. 2. reallocating processing of resources to regions involving in task performance 2. reallocating processing of resources to regions involving in task performance  This present study showed only deactivation in posterior midline regions were reduced, but enhanced in anterior midline regions by aging.  This present study showed only deactivation in posterior midline regions were reduced, but enhanced in anterior midline regions by aging.

Conclusion PASA pattern acts in a compensatory manner of offset posterior-related neuroanatomical declines due to aging and is generalizable to deactivations across both task and difficulty. PASA pattern acts in a compensatory manner of offset posterior-related neuroanatomical declines due to aging and is generalizable to deactivations across both task and difficulty.

Q: How could a region (eg. PFC) activate and deactivate simultaneously (see figure B&D)? If the regions of activation and deactivation are sort of different, is it proper to conclude more PFC activation and less occipital deactivation in older group?