Qué Qué PASA? The Posterior-Anterior PASA? The Posterior-Anterior Shift in AgingShift in Aging

Simon W. Davis, Nancy A. Dennis, Sander M. DSimon W. Davis, Nancy A. Dennis, Sander M. Daselaar, Mathias S. Fleck, & Roberto Cabezaaselaar, Mathias S. Fleck, & Roberto Cabeza

CerebralCerebral CortexCortex, doi:10.1093/cercor/bhm155, doi:10.1093/cercor/bhm155

BackgroundBackground

PASA (posterior-anterior shift in aging): PASA (posterior-anterior shift in aging):

1.1. an age-related reduction in occipital activity coupan age-related reduction in occipital activity coupled with increased frontal activity (Grady, 1994)led with increased frontal activity (Grady, 1994)

2.2. PASA pattern has found in attention, visual percPASA pattern has found in attention, visual perception, visuospatial processing, working memory,eption, visuospatial processing, working memory, episodic memory encoding & retrieval episodic memory encoding & retrieval

Unfinished issues of PASAUnfinished issues of PASA

Validity of PASA:Validity of PASA:

It may simply reflect difference in task difficulty (iIt may simply reflect difference in task difficulty (ic. objective & subject measures of difficulty), espc. objective & subject measures of difficulty), especially in its prefrontal cortex (PFC) component.ecially in its prefrontal cortex (PFC) component.

Function of PASA:Function of PASA: No study has found PFC activations in older adulNo study has found PFC activations in older adul

ts positively associated with performance and nets positively associated with performance and negatively associated with occipital activation gatively associated with occipital activation

Unfinished issues of PASAUnfinished issues of PASA──Cont.Cont. Generalizability of PASA:Generalizability of PASA:

PASA effect has been observed for activation, bPASA effect has been observed for activation, but not for deactivationut not for deactivation

Past findings showed attenuated deactivations in Past findings showed attenuated deactivations in posterior midline cortex in healthy older adults.posterior midline cortex in healthy older adults.

possibility: compensating this deficit by deactivapossibility: compensating this deficit by deactivating anterior midline regions to a greater extent tting anterior midline regions to a greater extent than younger adults?han younger adults?

Back to the current studyBack to the current study 3 predictions:3 predictions: 1. 1. PASA will exist even eliminating differences in difficPASA will exist even eliminating differences in diffic

ulty (the ulty (the validityvalidity of PASA) of PASA) 2. PFC activity will be positively correlated with cogniti2. PFC activity will be positively correlated with cogniti

ve performance and negatively correlated with occipve performance and negatively correlated with occipital activity, supporting the compensation account (thital activity, supporting the compensation account (the e functiofunction of PASA)n of PASA)

3. Older adults would show weaker deactivations in p3. Older adults would show weaker deactivations in posterior midline regions but stronger deactivations in osterior midline regions but stronger deactivations in anterior medial regions (the anterior medial regions (the generalizabilitygeneralizability of PAS of PASA)A)

MethodsMethods Participants: 12 younger Participants: 12 younger

& 12 older adults were & 12 older adults were matched by a rank order matched by a rank order based on corrected based on corrected scores of ER and VP scores of ER and VP performanceperformance

Methods-cont.Methods-cont.StimuliStimuli

For the episodic retrieval (ER) task:For the episodic retrieval (ER) task:

240 five-letter words & 80 five-letter pseudowords240 five-letter words & 80 five-letter pseudowords

For the visual perception (VP) taskFor the visual perception (VP) task

120 rectangles were divided by a jagged line to 2 are120 rectangles were divided by a jagged line to 2 areas, making different versions of a perceptual stimuli was, making different versions of a perceptual stimuli with different difficulty of subject performanceith different difficulty of subject performance

Methods-cont.Methods-cont.

Behavioral paradigmBehavioral paradigm

Prior to scanningPrior to scanning

**Showing intermixed real words and pseudowordsShowing intermixed real words and pseudowords

During scanningDuring scanning

** 4 runs of the ER & 2 runs of the VP task were perfor 4 runs of the ER & 2 runs of the VP task were performedmed

** accuracy & confidence were rated accuracy & confidence were rated

Methods-cont.Methods-cont.MRI scanningMRI scanning

** 4-T GE scanner was used.4-T GE scanner was used.

** The anatomical MRI was acquired using a 3D T1- w The anatomical MRI was acquired using a 3D T1- weighted echo-planar sequence.eighted echo-planar sequence.

fMRI analysesfMRI analyses

**Event-related blood oxygen level-dependent responsEvent-related blood oxygen level-dependent responses for each participant were analyzed using a modifiees for each participant were analyzed using a modified general linear modeld general linear model

ResultsResults Behavioral dataBehavioral data

Results-cont.Results-cont.

Neuroimaging resultsNeuroimaging results

Results-cont.Results-cont.

Neuroimaging results show PASA was found whNeuroimaging results show PASA was found when differences in task difficulty were eliminateden differences in task difficulty were eliminated

Results-cont.Results-cont. Neuroimaging results show in Neuroimaging results show in oldeolder adults PFC activity wr adults PFC activity w

as negatively correlated with activity in the occipital corteas negatively correlated with activity in the occipital cortex, but positively correlated with ER/VP performance; in x, but positively correlated with ER/VP performance; in yyoungerounger adults, no significant correlations between region adults, no significant correlations between regions or between activity and performances or between activity and performance

Results-cont.Results-cont.

Neuroimaging results indicated PASA was also fouNeuroimaging results indicated PASA was also found for deactivationnd for deactivation

DiscussionDiscussion

Validity of PASA: against a difficulty accountValidity of PASA: against a difficulty account

After removing difficulty difference, a clear PASA After removing difficulty difference, a clear PASA pattern was foundpattern was found──

** occipital activity: in younger > in older adults occipital activity: in younger > in older adults

** PFC activity: in older > in younger adults PFC activity: in older > in younger adults

Discussion-cont.Discussion-cont.

Function of PASA: for the compensation accountFunction of PASA: for the compensation account

**PFC activity compensates for the decrease in PFC activity compensates for the decrease in occipital activity that is necessary for successful occipital activity that is necessary for successful task performancetask performance

Discussion-cont.Discussion-cont. Generalizability of PASA: posterior-anterior shiGeneralizability of PASA: posterior-anterior shi

ft in deactivationsft in deactivations * “Default network”* “Default network”── previous studies indicated previous studies indicated 1. posterior and anterior midline cortices are often deactiv1. posterior and anterior midline cortices are often deactiv

ated during task compared with a resting baseline.ated during task compared with a resting baseline. 2. reallocating processing of resources to regions involvin2. reallocating processing of resources to regions involvin

g in task performanceg in task performance This present study showed only deactivation in posteriThis present study showed only deactivation in posteri

or midline regions were reduced, but enhanced in anteor midline regions were reduced, but enhanced in anterior midline regions by aging.rior midline regions by aging.

ConclusionConclusion

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

Q: Q: How could a region (eg. PFC) activate and How could a region (eg. PFC) activate and deactivate simultaneously (see figure B&D)? If the deactivate simultaneously (see figure B&D)? If the regions of activation and deactivation are sort of regions of activation and deactivation are sort of

different, is it proper to conclude more PFC activation different, is it proper to conclude more PFC activation and less occipital deactivation in older group?and less occipital deactivation in older group?