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You enter a crowded room, searching for an old friend amongst a sea of
unfamiliar faces and other distractions. You retrieve a stored
representation of your friend’s face from memory, hold it in mind and
compare it to the many faces before you. You scan your surroundings, making
lightening fast decisions… and soon a match is made and you recognize your
friend. As you cross the room another person waves at you, capturing your
attention. You signal that you will be right with them, and while storing
this new information in mind, you proceed to make contact with your friend.
Our brains receive a constant onslaught of sensory information that demands
a continuous integration between stimuli that capture our attention
independent of our goals (e.g., the person waving you over) and our internal
decisions as to where we direct our attention and what we store in memory
(e.g. searching the room for your friend and remembering the new face). The
focus of research in the Gazzaley lab is the neural process known as
top-down modulation, which
underlies our ability to exert conscious control over how we perceive our
environment. It is this ability to selectively focus our attention, suppress
distracting input and hold relevant information in mind that defines our
conscious experience and serves as a critical crossroad between attention
and memory. Furthermore, this phenomenon is not restricted to processing
visual information in crowded situations, as illustrated above, but it
occurs constantly and involves all of our senses. We would be incapable of
functioning if we were unable to exert conscious control over our perceptual
world. In fact, it is a breakdown of this system that leads to many of the
functional difficulties experienced by individuals as they age, as well as
those with dementia.
Although top-down modulation usually occurs
efficiently and with minimal effort, it involves complex interactions between
multiple brain regions – neural networks.
It is due to this complexity that critical details of this process remain poorly
understood. Moreover, this modulation is a bi-directional process, such that it
is necessary to both enhance visual
activity for relevant information and suppress
it for irrelevant information. For example, in order to find your friend in the
crowded room, activity in visual areas associated with your friend’s face is
enhanced as you identify them, while activity for the distracting irrelevant
information present throughout the room is suppressed.
Research in the Gazzaley lab focuses on furthering our understanding of the
neural mechanisms of top-down modulation (how
does it work?), alterations that occur in aging and neurological disease
(what goes wrong?) and how we may
intervene therapeutically when deficits occur (how
can we fix it?). To accomplish these goals, several human
neurophysiologic techniques are coupled: functional magnetic resonance imaging
(fMRI), electroencephalography (EEG) and transcranial magnetic stimulation
(TMS).
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