<b>I’ve been in my mind, it’s such a fine line. That keeps me searching for a heart of gold – Neil Young.</b>
There are many similarities between the human brain and the personal computer (PC). But while a PC has no problem executing a number of programs simultaneously, for the average human being, handling two things at once is much harder to do than handling one thing at a time.
But why should that be?
Two theories try to explain this phenomenon: “passive queuing” and “active monitoring.” The former says that information has to line up for a chance at being processed by the brain, while the latter suggests that the brain can process two things at once – it just needs to use a complicated mechanism to keep the two processes separate.
But which one is correct? Now, thanks to some recent research in the US, we might be closer to an explanation.
There, researchers Yuhong Jiang, Rebecca Saxe and Nancy Kanwisher at the Martinos Center for Biomedical Imaging examined the brain activity involved in ‘multitasking’. To do so, they gave people two simple tasks. Then, the subjects were forced to switch from one task to the other – either quickly or slowly. What they found was that, when people had to switch faster, they would take as much as twice as long to respond than when switching more slowly.
Using MRI technology, the researchers examined the brain activity of the individuals while performing these tasks. But they could find no increase in the sort of activity that would be involved in keeping two thought processes separate when their subjects had to switch faster.
Their results indicate that there are no complicated mechanisms that allow people to perform two tasks at once. Instead, they concluded that human beings are simply serial creatures that are better at performing the next task only after the last one is finished, with the inference that it’s passive queuing that’s taking place in the brain.
This isn’t the first time, of course, that MRI technology has been used to map brain activity. Last year, UCLA scientists evaluated the neural response of several individuals to a series of pictures depicting happiness, sadness, anger, surprise, disgust and fear. They were then able to figure out which areas of the brain were responsible for the creation of the emotions.
Undoubtedly, in the next few years, more brain mapping will lead us to a much greater understanding of how the human mind leads individuals to behave in the ways that they do. By then, it might even be possible for all of us to have our brains scanned by an MRI system and our very own unique ’emotional profile’ compressed and stored on something as portable as a Bluetooth enabled mobile phone.
Imagine the benefits! You could wave goodbye to dating for starters, ensuring the compatibility between yourself and any potential partners simply by comparing the activity of your brain profile with any one else that comes within range of your Bluetooth device.
Unfortunately, if more than one compatible person came along at once, the latest research on the incapacity of our brains to multitask would indicate that we are still going to have trouble coping with switching our attention quickly between the two.
If the emotional memory of a traumatic car accident or the thrill of first love are remembered with a special resonance, it is because they engage different brain structures than do normal memories, Duke University researchers have discovered.
Their new study provides clear evidence from humans that the brain’s emotional centre, called the amygdala, interacts with memory-related brain regions during the formation of emotional memories, perhaps to give such memories their indelible emotional resonance.
The researchers said their basic insights could contribute to understanding of the role that the neural mechanisms underlying emotional memory formation play in post traumatic stress disorder and depression.
The study by Florin Dolcos, Kevin LaBar and Roberto Cabeza was reported in the June 10, 2004 issue of the journal Neuron. Dolcos is a research associate in the Brain Imaging and Analysis Center and LaBar and Cabeza are, respectively, assistant and associate professors of psychological and brain sciences. They are also faculty in the Center for Cognitive Neurosciences. Their research was supported by the US National Institutes of Health.
According to Dolcos, in their experiments the researchers were seeking evidence for the “modulation hypothesis,” which holds that the brain’s emotional and memory centers interact during the formation of emotional memories.
“The basic idea was simple: to find evidence supporting the notion that the brain’s emotional region modulates activity in the memory regions to form an emotional memory,” said Dolcos. “This idea was supported by animal research, but the evidence from neurologically intact humans was scarce and indirect. So, our goal was to find the right method that would allow us to demonstrate that this phenomenon happens in humans, too,” he said.
In their study, the researchers sought to establish that the memory-enhancing effect of emotion is due to interaction between emotion- and memory-related brain regions. Thus, they first exposed volunteer subjects to a collection of pictures that evoked both positive and negative emotions and those that were neutral. Emotional pictures depicted such negative events as aggressive acts or injured people and such positive events as romantic scenes or sporting triumphs. Neutral pictures included such subjects as buildings or scenes of routine shopping.
While viewing the emotional and neutral pictures, participants’ brains were scanned using functional magnetic resonance imaging. Such imaging involves the use of harmless magnetic fields and radio signals to measure blood flow to individual brain regions, which reflects greater activity in those regions. Then, following the scanning session, the researchers tested participants’ memory for the images they viewed during the scanning.
Two important features distinguish the new study from previous functional neuroimaging studies, said the researchers. First, to identify the brain regions associated with the memory-enhancing effect of emotion, the study linked behavioral memory performance for emotional and neutral pictures to brain activity during memory formation. Second, to delineate the contribution of the emotion and memory-related regions during emotional memory formation, the study used precise anatomical methods, which involved tracing of these regions on each subject’s brain image.
As expected, analysis of the behavioral data revealed evidence that the memories of emotional images were more strongly encoded than the neutral ones. And importantly, the brain scans showed that the emotional memories evoked activity in the amygdala as well as the “medial temporal lobe memory” structures. Specifically, these structures include the hippocampus and associated regions. Moreover, according to Dolcos, the analysis revealed a significant correlation between the strength of activity in the emotion- and memory-related brain regions.
“We found evidence that the interaction between the emotional and memory regions occurred more systematically and consistently during the formation of emotional memories than during the formation of neutral memories,” Dolcos said. “More specifically, we found that the subjects showing greater successful encoding activity in the emotional region also had greater activity in the memory regions,” said Dolcos.
Said Cabeza of the findings, “Other studies have focused on the general enhancing effects of emotion on memory, and the evidence for the modulation hypothesis was disparate and inconclusive. Thus, this is the first direct evidence for the modulation hypothesis in humans and the first report of differences in sensitivity of the medial temporal lobe regions to encoding of emotional versus neutral stimuli.”
What’s more, said Cabeza, “We also found indications that some regions within the medial temporal lobe may actually be more specialized for encoding neutral information. We don’t know exactly what the processes involved are, or why these regions are engaged. But we speculate that the regions that were more activated for emotional stimuli are involved in semantic processing of the meaning of the images, whereas those that are more activated by neutral stimuli reflect perceptual processing.”
Thus, said Cabeza, the findings not only establish the functional link between the emotional and memory areas, but also hint at differences within the memory areas that should be explored with further studies. As part of their research, the authors are now exploring the role of these brain regions during the retrieval of well-consolidated emotional memories.
While such studies are basic in nature, said Cabeza, better delineation of the role of the amygdala in emotional memory could aid understanding of post traumatic stress disorder – especially such phenomena as flashbacks of traumatic memories.
Said Dolcos, “Also, people who suffer depression ruminate obsessively on negative or unpleasant memories. This problem could reflect a pathology in how their memory systems have processed emotional memories.”
Thus, said Cabeza, he and his collaborators are now exploring the nature of emotional memory encoding in people with depression, before and after therapy.