Zicong

2012-7-9

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Corresponding author

NORMAN M. WEINBERGER• Research Professor

• Center for the Neurobiology of Learning and Memory,

Dept. of Neurobiology and Behavior, University of California, Irvine.

• Research interests: acquisition, retention and representation of information in the cerebral cortex that underlie behavioral memory

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The hypothesis

• Experience-based activation of the nucleus basalis (NB) (which is the major source of cortical ACh), is engaged in the formation of at least some types of behavioral memory.

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The hypothesis

• Activation of the cholinergic nucleus basalis serves as a ‘‘final common path’’ that is sufficient to promote or induce long-term memory based on the formation of information storage in the cerebral cortex, and perhaps elsewhere.

• The nucleus basalis is ‘‘downstream’’ of motivational and emotional systems.

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Background

• The initial study revealed that pairing a tone with NBstm produced associative memory.

• The putative implanted memory shares the cardinal features of natural associative memory, including specificity, rapid development, consolidation and retention and that NBstm was motivationally neutral.

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In this study

• The goal of this experiment was to determine if it exhibits a critical feature of natural associative memory, viz., long-term retention, herein defined as maintenance of specific memory for 2 weeks.

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Methods

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Methods

Tone: 1.00, 2.75, 4.50, 6.25, 8.00, 9.75, 11.50, 13.25, 15.00 kHz, cosine 10 ms rise/fall time (10-90%), 70 dB SPLc

NBstm: ~65 uA, pairs of 0.2 ms opposite polarity pulses, 100 Hz, 200 ms trains

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MethodsLFP recording site

NB stimulation sites

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Methods

Respiration changes and RCI (second-by-second)

EEG of A1

Respiration Change Index (RCI): RCIi = (|Posti–Pre|)/(Posti + Pre)Post and Pre were the values of power of respiration signal

Autocorrelation function (AC): 0.700<AC<0.975 indicating the quiescent behavioral state

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Results

RCI changes

Between-group differences (Paired minus unpaired)

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Results

Changes in response to individual frequencies within the CS-band

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Results

• The Paired group had acquired a CS-specific associative memory following pairing of tone with NBstm.

• 2 weeks later: 1) responses to all nine test tones became strong

er; 2) responses at the CS-band become stronger; 3) within the CS-band, only responses to the CS

become stronger; 4) the memory had generalized to the low freque

ncy band.

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Discussion

• specific associative memory induced by pairing a tone with NBstm exhibits long-term retention.

• the specificity of this memory consolidates over a 2-week period, and in so doing exhibits both increased specificity for the CS frequency and a general reduction in specificity across the frequency domain.

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Discussion

• We suggest that the contents of memory implanted in this study are that a particular tonal frequency (or range of frequencies) is behaviorally important but that the normal reason for this importance is absent.

• In other words, certain sounds are now stored in the brain as more relevant or salient to the animal than otherwise despite the absence of any actual natural experience that would render them of increased significance.