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N M Weinberger

Publications and source records attributed to N M Weinberger.

At least 19 recordsLinked to original sources
PubMed1995

Heterosynaptic long-term facilitation of sensory-evoked responses in the auditory cortex by stimulation of the magnocellular medial geniculate body in guinea pigs.

The magnocellular nucleus of the medial geniculate body (MGm) develops physiological plasticity during classical conditioning and may be involved in learning-induced receptive field plasticity in the auditory cortex. To determine the ability of the MGm to produce long-term modification of evoked activity in the auditory cortex, the experimenters paired electrical stimulation of the MGm with preceding clicks in adult guinea pigs under barbiturate anesthesia. The amplitudes of average click-evoked potentials were significantly facilitated in all subjects. Facilitation endured for 2 hr, the maximum duration of recording. Sham-stimulated control guinea pigs did not develop facilitation. Thus, a nonlemniscal thalamic sensory nucleus can produce enduring facilitation of sensory-evoked activity in primary sensory cortex, suggesting that long-term physiological plasticity in the sensory cortex during learning may involve nonlemniscal thalamic mechanisms.

Animals↗
PubMed1992

Frequency selectivity is related to temporal processing in parallel thalamocortical auditory pathways.

Lemniscal and non-lemniscal parallel thalamocortical auditory pathways have been identified with the ventral medial geniculate body (MGB) vs. the dorsal and medial MGB, respectively. Lemniscal neurons have narrow frequency tuning and provide highly specific frequency information to the auditory cortex whereas non-lemniscal neurons generally have broader tuning and greater response lability, including plasticity of frequency receptive fields during learning. To determine if frequency selectivity is related to temporal fidelity of response, we measured both the breadth of tuning and neuronal excitability in a paired tone paradigm for single neurons throughout the MGB. Excitability to the second tone of a pair was directly correlated with frequency selectivity: the narrower the frequency tuning, the greater the excitability. Cells with broad tuning based on multiple-peak response areas also were less excitable than cells with single-peak RAs. Cells in the ventral MGB showed greater temporal fidelity of response (greater excitability) than cells in the dorsal and medial MGB. These findings show that high degrees of both frequency selectivity and temporal response fidelity are characteristic of the lemniscal, but not the non-lemniscal, thalamocortical auditory system.

Acoustic Stimulation↗
PubMed1992

Sensitization induced receptive field plasticity in the auditory cortex is independent of CS-modality.

Sensitization training with an auditory stimulus produces a general increase in response magnitude across the entire receptive field (RF) of neurons in the primary auditory cortex of the guinea pig (Bakin, J.S. and Weinberger, N.M., Brain Res., 536 (1990) 271-286). To determine if this effect reflects an auditory system-specific process or is caused by a process independent of the training stimulus modality, RFs in primary auditory cortex were characterized before and immediately after adult guinea pigs were given sensitization training with either an auditory or a visual training stimulus. General increases in auditory response magnitude across the RF were observed in 7 out of 7 auditory sensitization cases and 4 out of 5 visual sensitization cases. There were no statistical differences between the effects of auditory and visual sensitization training. These findings indicate that the general increases observed following sensitization training are the result of processes independent of CS modality, in contrast to the highly specific RF modifications that are caused by classical conditioning. The findings suggest that the 2 forms of RF plasticity, CS-specific re-tuning due to associative conditioning and polymodal general increases in gain due to non-associative sensitization, may reflect neural mechanisms involved in selective attention and vigilance, respectively.

Acoustic Stimulation↗
PubMed1992

Synaptic potentials and effects of amino acid antagonists in the auditory cortex.

Neurons of in vitro guinea pig and rat auditory cortex receive a complex synaptic pattern of afferent information. As many as four synaptic responses to a single-stimulus pulse to the gray or white matter can occur; an early-EPSP followed, sequentially, by an early-IPSP, late-EPSP, and late-IPSP. Paired pulse stimulation and pharmacological studies show that the early-IPSP can modify information transmission that occurs by way of the early-EPSP. Each of these four synaptic responses differed in estimated reversal potential, and each was differentially sensitive to antagonism by pharmacological agents. DNQX (6,7-dinitroquinoxaline-2,3-dione), a quisqualate/kainate receptor antagonist, blocked the early-EPSP, and the late-EPSP was blocked by the NMDA receptor antagonist APV (D-2-amino-5-phosphonovalerate). The early-IPSP was blocked by the GABA-a receptor antagonist bicuculline, and the late-IPSP by the GABA-b receptor antagonists 2-OH saclofen or phaclofen. Presentation of stimulus trains, even at relatively low intensities, could produce a long-lasting APV-sensitive membrane depolarization. Also discussed is the possible role of these synaptic potentials in auditory cortical function and plasticity.

Amino Acids↗
PubMed1992

Associative retuning in the thalamic source of input to the amygdala and auditory cortex: receptive field plasticity in the medial division of the medial geniculate body.

The medial division of the medial geniculate body (MGm) projects to the lateral amygdala and the upper layer of auditory cortex and develops physiological plasticity rapidly during classical conditioning. The effects of learning on frequency receptive fields (RFs) in the MGm of the guinea pig have been determined. Classical conditioning (tone-footshock), as indexed by rapid development of conditioned bradycardia, produced conditioned stimulus (CS)-frequency specific RF plasticity: increased response at the CS frequency with decreased responses at other frequencies, both immediately and after a 1-hr retention period. Sensitization training produced only general changes in RFs. These findings are considered with reference to both the elicitation of amygdala-mediated, fear-conditioned responses and the mechanism of retrieval of information stored in the auditory cortex during acquisition.

Amygdala↗
PubMed1992

Stimulation at a site of auditory-somatosensory convergence in the medial geniculate nucleus is an effective unconditioned stimulus for fear conditioning.

The medial division of the medial geniculate nucleus (MGm) and the posterior intralaminar nucleus (PIN) are necessary for fear conditioning to an auditory conditioned stimulus (CS), receive both auditory and somatosensory input, and project to the amygdala, which is involved in production of fear conditioned responses. If CS-unconditioned stimulus (US) convergence in the MGm-PIN is critical for fear conditioning, then microstimulation of this area should serve as an effective US during classical conditioning, in place of standard footshock. Guinea pigs underwent conditioning (40-60 trials) using a tone as the CS and medial geniculate complex microstimulation as the US. Conditioned bradycardia developed when the US electrodes were in the PIN. However, microstimulation was not an effective US for conditioning in other parts of the medial geniculate or for sensitization training in the PIN or elsewhere. Learning curves were similar to those found previously for footshock US. Thus, the PIN can be a locus of functional CS-US convergence for previously for footshock US. Thus, the PIN can be a locus of functional CS-US convergence for fear conditioning to acoustic stimuli.

Amygdala↗
PubMed1992

Frequency-specific receptive field plasticity in the medial geniculate body induced by pavlovian fear conditioning is expressed in the anesthetized brain.

Fear conditioning modifies the processing of frequency information; receptive fields (RF) in the auditory cortex and the medial geniculate body (MGB) are altered to favor processing the frequency of the conditioned stimulus (CS) over the pretraining best frequency (BF) and other frequencies. This experiment was designed to determine whether brief conditioning in the waking state produces RF plasticity that is expressed under general anesthesia. Guinea pigs bearing electrodes in the MGB received 20 trials of tone-shock pairing in a single training session. RFs were determined with animals under ketamine anesthesia before conditioning and 1-3 hr and 24 hr after conditioning. Frequency-specific RF plasticity was evident for both postconditioning periods: The BF shifted toward or to the CS frequency, responses to the BF decreased, and responses to the CS increased. Broadly tuned cells developed greater RF plasticity than narrowly tuned neurons. The results demonstrate that the specific neuronal results of brief learning experiences can be expressed in the anesthetized brain.

Amygdala↗
PubMed1991

Subcortical adaptive filtering in the auditory system: associative receptive field plasticity in the dorsal medial geniculate body.

Highly specific subcortical receptive field (RF) plasticity was found in the dorsal division of the guinea pig medial geniculate body during cardiac conditioning to a tonal frequency. There was increased response to the conditioned-stimulus (CS) frequency, and there were decreased responses to adjacent frequencies, especially at the pretraining best frequency (BF), which often resulted in a shift of tuning such that the CS became the new BF. Moreover, 1 hr later the effects were stronger, more sharply tuned, and centered on the CS frequency. A sensitization paradigm produced only broad, general increases of response across the RF. These findings reveal that the analysis of sensory RF dynamics is a valuable approach to understanding the neural mechanisms of information processing in learning and memory.

Animals↗
PubMed1991

Habituation produces frequency-specific plasticity of receptive fields in the auditory cortex.

Associative learning produces conditioned stimulus (CS)-specific plasticity of frequency receptive fields (RFs) in the auditory cortex; responses to the CS frequency are increased, whereas responses to other frequencies are decreased. This study determined the effects of habituation on the RF of neurons in the auditory cortex of the guinea pig (Cavia porcellus). One frequency was presented repeatedly (REP) followed by redetermination of the RF. After REP, 26/36 (72%) RFs exhibited a substantial reduction (70-75%) of response to the repeated frequency, and this was highly specific (bandwidth less than 0.125 octave). This RF plasticity involves an initial decrease in response during REP but does not require attenuated responses at the end of REP. Incubation (i.e., development over time after cessation of REP) and long-term frequency-specific effects are evident. Thus, habituation induces a specific change in the processing of frequency information rather than a general reduction in responsivity.

Acoustic Stimulation↗
PubMed1991

Thalamic short-term plasticity in the auditory system: associative returning of receptive fields in the ventral medial geniculate body.

The effects of classical conditioning on frequency receptive fields (RFs) in the ventral, tonotopic part of the guinea pig (Cavia porcellus) medial geniculate ventral body (MGv) during cardiac conditioning to a single tone frequency were studied. Associative frequency-specific plasticity, in which the RF was returned to the frequency of the conditioned stimulus (CS), developed if the CS frequency was within 0.125 octave of the pretraining best frequency. Otherwise, a general increase across the RF developed. Sensitization training also produced general increased responses. The frequency-specific plasticity was short-term and observed only immediately after training, whereas the general effects were maintained. These results suggest that frequency-specific RF plasticity in the MGv may be a substrate of short-term mnemonic processes that could participate in long-term storage of information and modification of the representation of the CS at the auditory cortex.

Animals↗
PubMed1990

Classical conditioning induces CS-specific receptive field plasticity in the auditory cortex of the guinea pig.

To determine if classical conditioning produces general or specific modification of responses to acoustic conditioned stimuli (CS), frequency receptive fields (RF) of neurons in guinea pig auditory cortex were determined before and up to 24 h after fear conditioning. Highly specific RF plasticity characterized by maximal increased responses to the CS frequency and decreased responses to the pretraining best frequency (BF) and other frequencies was observed in 70% of conditioning cases. These opposing changes were often sufficient to produce a shift in tuning such that the frequency of the CS became the new BF. CS frequency specific plasticity was maintained as long as 24 h. Sensitization training produced general increased responses across the RF without CS specificity. The findings indicate that associative processes produce systematic modification of the auditory system's processing of frequency information and exemplify the advantages of combining receptive field analysis with behavioral training in the study of the neural bases of learning and memory.

Acoustic Stimulation↗
PubMed1990

Cholinergic modulation of responses to single tones produces tone-specific receptive field alterations in cat auditory cortex.

Acetylcholine (ACh), acting via muscarinic receptors, is known to modulate neuronal responsiveness in primary sensory neocortex. The administration of ACh to cortical neurons facilitates or suppresses responses to sensory stimuli, and these effects can endure well beyond the period of ACh application. In the present study, we sought to determine whether ACh produces a general change in sensory information processing, or whether it can specifically alter the processing of sensory stimuli with which it was "paired". To answer this question, we restricted acoustic stimulation in the presence of ACh to a single frequency, and determined single neuron frequency receptive fields in primary auditory cortex before and after this pairing. During its administration, ACh produced mostly facilitatory effects on spontaneous activity and on responses to the single frequency tone. Examination of frequency receptive fields after ACh administration revealed receptive field modifications in 56% of the cells. In half of these cases, the receptive field alterations were highly specific to the frequency of the tone previously paired with ACh. Thus ACh can produce stimulus-specific modulation of auditory information processing. An additional and unexpected finding was that the type of modulation during ACh administration did not predict the type of receptive field modulation observed after ACh administration; this may be related to the physiological "context" of the same stimulus in two different conditions. The implications of these findings for learning-induced plasticity in the auditory cortex is discussed.

Acetylcholine↗
PubMed1990

Acetylcholine modifies neuronal acoustic rate-level functions in guinea pig auditory cortex by an action at muscarinic receptors.

Cholinergic modification of neuronal responsiveness in auditory cortex includes alteration of spontaneous and tone-evoked neuronal discharge. Previously it was suggested that the effects of acetylcholine (ACh) and muscarinic agonists on neuronal discharge resembled those due to increases in the intensity of acoustic stimuli (Ashe et al. 1989). To determine the relationship between neuronal modifications due to ACh acting at muscarinic receptors and those due to changes in stimulus intensity, we determined acoustic rate-level functions for neurons in the auditory cortex of barbiturate-anesthetized guinea pigs before, during and after administration of ACh. ACh facilitated acoustic rate-level functions in 82% of the cells tested. In addition, during ACh administration 66% of neurons responded to stimuli that were previously subthreshold, that is, ACh decreased the response threshold. Cholinergic facilitation of rate-level functions was attenuated by the general muscarinic antagonist atropine. The nature of the muscarinic receptors involved in the actions of ACh was further examined by presenting single tones before, during, and after administration of ACh and specific muscarinic receptor subtype antagonists, either pirenzepine (M1) or gallamine (M2). ACh-induced facilitation of spontaneous and tone evoked neuronal discharge was antagonized by pirenzepine, but not by gallamine, suggesting the involvement of the M1 muscarinic receptor subtype. These data indicate that ACh can facilitate stimulus-evoked responses and decrease response thresholds for neurons in auditory cortex, possibly via activation of M1 muscarinic receptors. Such effects of ACh acting at muscarinic receptors could underly cholinergic regulation of information processing in the auditory cortex.

Acetylcholine↗
PubMed1989

Responses of single auditory cortical neurons to tone sequences.

The responses of single neurons in the primary and secondary auditory cortex of cat were recorded during the presentation of sequences consisting of five tones of different frequencies. Discharges to tones within these sequences usually (84%) exhibited a dependence on the 'direction' of the sequence (ascending, descending, or mixed frequencies). For sequences consisting of 5 tones of identical frequency (monotone) the response often depended on serial position, including cases in which the neuron only responded to later tones in the sequence. Comparison of responses to heterogeneous and monotone sequences showed that response dependence on serial position was a factor in response dependence on sequence direction. Auditory cortical neurons can exhibit stronger responses to a tone presented in a sequence than to the same tone presented alone. Hence, the responses to tones within sequences may not be highly predictable from the responses to isolated tones.

Acoustic Stimulation↗
PubMed1989

Acetylcholine produces stimulus-specific receptive field alterations in cat auditory cortex.

Frequency receptive fields (RFs) were determined before and after pairing iontophoretic administration of acetylcholine (ACh) with a repeated single-frequency stimulus in the auditory cortex of barbiturate-anesthetized cats. In 58% of the cells, the paired ACh + tone treatment produced subsequent alterations of frequency RFs. In half of these cases, the RF modifications were highly specific to the frequency that had been paired with ACh. Atropine antagonized the frequency-specific effects of ACh, suggesting that they were mediated via muscarinic cholinergic receptors.

Acetylcholine↗
PubMed1989

Cholinergic modulation of frequency receptive fields in auditory cortex: I. Frequency-specific effects of muscarinic agonists.

Previously we reported that acetylcholine (ACh) and acetyl-beta-methacholine (MCh) modify responses of neurons in auditory cortex to individual frequencies. The purpose of this study was to determine whether muscarinic agonists produce frequency-specific alterations or general changes in cellular responses. Frequency-specific modifications would be evident in alterations of frequency receptive fields (FRF) that differed across frequencies while general effects would be seen as changes that were more or less the same over frequencies. Responses of single neurons to designated sets of tones were recorded in the auditory cortex of chronically prepared awake cats before, during, and following ejection of ACh or MCh by iontophoresis or micropressure using multibarrel micropipettes. Frequency receptive fields were determined by presenting isointensity tones across a range of frequencies including the cell's best frequency (BF) to tone onset. FRF for "off" and "sustained (through)" responses were also determined quantitatively. The effects of ACh and MCh were predominantly frequency-specific (77%, 39/51 cells); general changes (19%, 10/51) and no effects (4%, 2/51) were less likely. Frequency-specific effects involved both facilitation and reduction of the same response component to different frequencies within the same neuron. For responses to tone onset (but not "through" and "off" responses), agonists were more likely to produce a decrease at the BF while simultaneously increasing responses to other frequencies. Agonists could increase or decrease frequency selectivity. Effects of agonists could be blocked by atropine, suggesting involvement of muscarinic receptors.

Acetylcholine↗