Study: fMRI pinpoints visual & acoustic memory to common brain region
Researchers have used fMRI to identify the left intraparietal sulcus as active in working memory for both visual and acoustic sensory inputs, complementing past imaging research indicating that individual brain regions can be responsible for multi-sensory functions, according to a study published in the Journal of Cognitive Neuroscience.
Previous fMRI research has observed increased activation in the intraparietal sulcus (IPS) in response to an increase in the number of visual memoranda, establishing that the IPS is thoroughly involved in working memory. Moreover, studies have also shown that individual regions of interest can be involved in perception and working memory from multiple sensory modalities.
In an effort to wed these insights, the present authors were the first to acquire fMRI images of combined acoustic verbal and visual nonverbal working memory tasks. “The present research goal is simply to establish whether at least one brain area responds to both visual nonverbal and acoustic verbal working memory items in a manner robust enough to survive across two experiments,” wrote Nelson Cowan, PhD, and colleagues from the Brain Imaging Center, department of psychological sciences, at the University of Missouri in Columbia.
The researchers performed two working memory experiments. In the first, 16 participants were presented with either two or four visual or acoustic stimuli (colored squares or spoken letters) and probed to recall the stimuli. The second experiment consisted of similar procedures, new participants and an added caveat: subjects were additionally presented with just two acoustic stimuli in addition to the other objects, as opposed to acoustic stimuli presented always concomitantly with visual ones. This procedure was added to ensure that, if a certain brain region were involved in both visual and acoustic memory, it was in fact indicative of a multi-sensory function, rather than a region of interest that was activated only because the brain was at full memory capacity (individuals have been shown to remember a maximum of four objects under the present experimental conditions). All 120 test trials for experiment one and 160 for experiment two were assessed via fMRI.
The researchers observed an increased blood oxygen-level dependent (BOLD) signal from the left IPS whenever memory load (two or four stimuli) increased for visual, acoustic and visual-acoustic trials. Moreover, as acoustic and visual loads dropped (to two cards or words), BOLD signal weakened.
“The present finding is remarkable in that a single brain region was found to be involved in working memory maintenance regardless of the modality of the stimuli to be maintained, across two experiments with different methodologies,” Cowan and co-authors explained. “Further, the area that emerged, completely on an empirical basis, was the left IPS, one of just a few areas pointed out as a possible basis of visual working memory in previous studies. In short, the left IPS may be a special basis of working memory storage for items in both modalities.”
Passing beyond the identification of the left IPS in multi-sensory working memory, the researchers were unclear as to the functionality of the region, whether the IPS holds item information or merely pointers to other regions holding that information. The authors called on additional studies to bring researchers closer to this conclusion.
“Highlighting the role of abstraction in memory and learning, the present results appear to require a departure from the traditional view of working memory, which included only phonological and visual storage mechanisms. There is some kind of maintenance within the working memory system that is more general or abstract, and here we have begun to identify its neural basis,” Cowan and colleagues concluded.
Previous fMRI research has observed increased activation in the intraparietal sulcus (IPS) in response to an increase in the number of visual memoranda, establishing that the IPS is thoroughly involved in working memory. Moreover, studies have also shown that individual regions of interest can be involved in perception and working memory from multiple sensory modalities.
In an effort to wed these insights, the present authors were the first to acquire fMRI images of combined acoustic verbal and visual nonverbal working memory tasks. “The present research goal is simply to establish whether at least one brain area responds to both visual nonverbal and acoustic verbal working memory items in a manner robust enough to survive across two experiments,” wrote Nelson Cowan, PhD, and colleagues from the Brain Imaging Center, department of psychological sciences, at the University of Missouri in Columbia.
The researchers performed two working memory experiments. In the first, 16 participants were presented with either two or four visual or acoustic stimuli (colored squares or spoken letters) and probed to recall the stimuli. The second experiment consisted of similar procedures, new participants and an added caveat: subjects were additionally presented with just two acoustic stimuli in addition to the other objects, as opposed to acoustic stimuli presented always concomitantly with visual ones. This procedure was added to ensure that, if a certain brain region were involved in both visual and acoustic memory, it was in fact indicative of a multi-sensory function, rather than a region of interest that was activated only because the brain was at full memory capacity (individuals have been shown to remember a maximum of four objects under the present experimental conditions). All 120 test trials for experiment one and 160 for experiment two were assessed via fMRI.
The researchers observed an increased blood oxygen-level dependent (BOLD) signal from the left IPS whenever memory load (two or four stimuli) increased for visual, acoustic and visual-acoustic trials. Moreover, as acoustic and visual loads dropped (to two cards or words), BOLD signal weakened.
“The present finding is remarkable in that a single brain region was found to be involved in working memory maintenance regardless of the modality of the stimuli to be maintained, across two experiments with different methodologies,” Cowan and co-authors explained. “Further, the area that emerged, completely on an empirical basis, was the left IPS, one of just a few areas pointed out as a possible basis of visual working memory in previous studies. In short, the left IPS may be a special basis of working memory storage for items in both modalities.”
Passing beyond the identification of the left IPS in multi-sensory working memory, the researchers were unclear as to the functionality of the region, whether the IPS holds item information or merely pointers to other regions holding that information. The authors called on additional studies to bring researchers closer to this conclusion.
“Highlighting the role of abstraction in memory and learning, the present results appear to require a departure from the traditional view of working memory, which included only phonological and visual storage mechanisms. There is some kind of maintenance within the working memory system that is more general or abstract, and here we have begun to identify its neural basis,” Cowan and colleagues concluded.