Biomedical subjects
Stuart M Zola
Publications and source records attributed to Stuart M Zola.
Neural correlates of knowledge: stable representation of stimulus associations across variations in behavioral performance.
Behavioral responses to a sensory stimulus are often guided by associative memories. These associations remain intact even when other factors determine behavior. The substrates of associative memory should therefore be identifiable by neuronal responses that are independent of behavioral choices. We tested this hypothesis using a paired-associates task in which monkeys learned arbitrary associations between pairs of visual stimuli. We examined the activity of neurons in inferior temporal cortex as the animals prepared to choose a remembered stimulus from a visual display. The activity of some neurons (22%) depended on the monkey's behavioral choice; but for a novel class of neurons (54%), activity reflected the stimulus that the monkey was instructed to choose, regardless of the behavioral response. These neurons appear to represent memorized stimulus associations that are stable across variations in behavioral performance. In addition, many neurons (74%) were modulated by the spatial arrangement of the stimuli in the display.
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Selective neurotoxic amygdala lesions in monkeys disrupt reactivity to food and object stimuli and have limited effects on memory.
Monkeys with bilateral neurotoxic amygdala lesions and normal monkeys were administered tests of emotional reactivity, recognition memory, and reward association memory. There were 3 main findings. First, monkeys with amygdala lesions performed differently than normal monkeys on initial administrations of the emotional reactivity tests and on retests that were given 21-23 months after surgery. Second, they performed like normal monkeys on tests of recognition memory. Third, they were initially impaired on a test of reward association memory, but they were not impaired on a retest that was given 16 months after surgery. These findings underscore the role of the amygdala in aspects of emotional reactivity and reward association memory, but not in recognition memory. In addition, at least some of the behavioral effects of amygdala damage can be long lasting.
Anterograde amnesia and temporally graded retrograde amnesia for a nonspatial memory task after lesions of hippocampus and subiculum.
We studied the importance of the hippocampus and subiculum for anterograde and retrograde memory in the rat using social transmission of food preference, a nonspatial memory task. Experiment 1 asked how long an acquired food preference could be remembered. In experiment 2, we determined the anterograde amnesic effects of large lesions of the hippocampus that included the subiculum. In experiment 3, large lesions of the hippocampus that included the subiculum were made 1, 10, or 30 d after learning to determine the nature and extent of retrograde amnesia. Normal rats exhibited memory of the acquired food preference for at least 3 months after learning. Hippocampal lesions that included the subiculum produced marked anterograde amnesia and a 1-30 d temporally graded retrograde amnesia. The results show the importance of the hippocampus and related structures for nonspatial memory and also demonstrate the temporary role of these structures in long-term memory.