Nature Neuroscience pp 1298 - 1300

Older people may be worse at remembering things because they have trouble suppressing irrelevant information, reports a new functional imaging study from Adam Gazzaley and colleagues in the October issue of Nature Neuroscience.

Older and younger subjects had their brains scanned with MRI while they viewed faces and scenes, with instructions either to remember the scenes and ignore the faces, or vice-versa. When asked to remember scenes, both younger and older subjects had increased activity in the left parahippocampal/lingual gyrus, a brain area that normally processes scenes.

When told to ignore the scenes and remember faces instead, the younger subjects showed reduced activity in these same areas. Older subjects did not show such activity reductions, indicating a deficit in suppressing information not needed for the task. The older subjects were also worse at recalling previously viewed pictures. Some older subjects were able to perform the task well and their brain activity was more similar to that of younger subjects, with reduced activation in scene-processing areas when scenes were to be ignored.

Nature Neuroscience pp 1393 - 1402

When two different images or words are seen within half a second of each other, the second image or word is very difficult to consciously detect. A new study in the October issue of Nature Neuroscience suggests that the earlier the first image reaches conscious awareness, the more likely it is that we will also consciously perceive the second.

Claire Sergent and colleagues recorded electrical brain activity while people indicated whether they had seen the second of two quickly presented targets. They found an early wave of activity that occurred after each target, whether or not people reported seeing it. In contrast, a later wave, appearing around 300 milliseconds after each target, only occurred when a target was consciously detected - spreading through a network of many brain areas thought to be involved in consciousness. The sooner the appearance of the late wave associated with the first target, the more likely it was that the second target would be consciously perceived. These findings provide further information about the sequence and timing of brain processes that differentiate conscious and unconscious perception.