HAROLD

HAROLD is an acronym for Hemispheric Asymmetry Reduction in Older Adults. It is also the name for a model that contends that activity in the Pre-frontal Cortex is less lateralized in older than in younger adults.1 Remember the specialization of the cerebral hemispheres. The left hemisphere is more specialized for the processing of verbal information, and the right hemisphere is more specialized for the processing of visual-spatial information. According the the HAROLD model this lateralization of function reduces as we age. Electrophysiological, fMRI, (see the blog, “How Can the Brain Be Imaged” to learn about these techniques) and behavioral evidence support this model in a wide variety of domains in both memory and perception. In one study young adults showed right PFC activations during word pair cued recall, whereas older adults showed significant activations in both both right and left PFC. The notion here is that this bilateral pattern of PFC is compensatory. That is, to counteract cognitive decline, older adults recruited both hemispheres whereas young adults recruited mainly one hemisphere. Similar age-related asymmetry reductions during retrieval have been found for other tasks to include word stem cued recall, word recognition, and face recognition. So HAROLD has been demonstrated for both recall and recognition tasks for both verbal and nonverbal materials during retrieval.2

Age-related asymmetry reductions have also been found during memory storage. Older adults still show a lack of hemispheric asymmetry when they are provided with strategies that raise their PFC activities to the level of young adults. So HAROLD has been shown for both information storage and retrieval.

HAROLD has also been shown for verbal vs. spatial asymmetries. PFC activity tends to be left lateralized for verbal working memory and right lateralized for spatial working memory. Older adults showed significant PFC activity bilaterally for both verbal and spatial symmetry. A reasonable question to ask is what is meant by older adults. Sometimes older participants are under the age of 50 and still show effects predicted by the HAROLD model. However, research does indicate that HAROLD does become more pronounced with advancing age.3

HAROLD indicates an age-related increase in hemispheric cooperation. A compelling view is that this cooperation is a compensation mechanism for age-related decline. That is, to counteract cognitive decline, older adults recruit both hemispheres during task conditions for which young adults primarily recruit one hemisphere. One study had participants match two letters projected either to the same visual field (hemisphere) in which the comparison could be done within the hemisphere. Or the projection was made to opposite visual fields (hemispheres)., in which the comparisons had to be made between hemispheres. The letter matchings involved three levels of difficulty:  low (physical matching with one distractor), medium (physical matching with three distractors), and high (name matching with three distractors). Here the critical comparisons are the reaction time differences between the within- and cross-hemisphere conditions. For young adults, the within-hemisphere was faster when difficulty was low, and the across-hemisphere conditions was faster when difficulty was high. The two conditions did not differ significantly when the difficulty was medium. The interpretation here is that at high levels of difficulty, the benefits of engaging resources from both hemispheres outweigh the costs of interhemisphereic communication. For the old adults the benefits of bihemispheric processing became evident at moderate levels of difficulty. Thus, the old adults benefited from interhemispheric processing earlier than the young adults, suggesting that old adults rely more on interhemispheric processing than do young adults.4

 


1Cabeza, R. ((2002).  Hemispheric asymmetry reduction in older adults:  The Harold model.  Psychology and Aging, 17, 85-100.

2Cabeza, R., Nyberg, L., & Park, D. (2005).  op. cit. p. 334.

3Cabeza, R., Nyberg, L., & Park, D. (2005).  op. cit. p. 334-335.

4Cabeza, R., Nyberg, L., & Park, D. (2005).  op. cit. p. 338-340.

© Douglas Griffith and healthymemory.wordpress.com, 2009. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

 

Advertisements

Tags: ,

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


%d bloggers like this: