Gating Deficits

In a world where we are simultaneously bombarded with a great deal of stimulation, we learn to focus our attention on important stimuli, while filtering out (gating) less relevant simulation. Patients with schizophrenia not only have difficulties focusing their attention on important stimuli, they also have difficulties filtering out irrelevant stimuli, rendering them continually overwhelmed by their environment.

Pre-Pulse Inhibition (PPI) is a paradigm commonly used to measure these gating deficits in schizophrenia patients. In this paradigm, a person's excitatory responses to loud stimuli are measured. Exposure to a loud stimulus will elicit a large excitatory response. Exposure to a soft stimulus (pre-pulse) immediately before the loud stimulus will cause a much smaller excitatory response to the loud stimulus. A ratio of the size of the second response to the first is inversely proportional to the strength of the inhibition. By placing a number of electrodes at distinct locations on the scalp, an electrically positive evoked potential (P50) can be recorded 50 msec after the presentation of the loud stimulus. This P50 response to the loud auditory stimulus is normally diminished when the loud stimulus is immediately (500 m sec) preceded by the soft stimulus in the pre-pulse condition. In patients with schizophrenia, the amplitude of the P50 auditory-evoked response is not diminished in the pre-pulse condition, indicating an inability to gate sensory information (Light and Braff, 1999). These gating deficits are thought to be due, at least in part, to disruptions in the hippocampus since the P50-evoked potential is thought to originate from this brain region.

Interestingly, many family members of patients with schizophrenia also show gating deficits without having any clinical signs of the disease. It seems therefore that gating deficits may be genetically inherited as one of the symptoms of schizophrenia that alone may be no more than a subtle cognitive abnormality.

Anxiety and Depression 101

Anxiety and Depression 101

Everything you ever wanted to know about. We have been discussing depression and anxiety and how different information that is out on the market only seems to target one particular cure for these two common conditions that seem to walk hand in hand.

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