title: Higher-Order Sensory Cortex Drives Basolateral Amygdala Activity during the Recall of Remote, but Not Recently Learned Fearful Memories.
abstract: Negative experiences are quickly learned and long remembered. Key unresolved issues in the field of emotional memory include identifying the loci and dynamics of memory storage and retrieval. The present study examined neural activity in the higher-order auditory cortex Te2 and basolateral amygdala (BLA) and their crosstalk during the recall of recent and remote fear memories. To this end, we obtained local field potentials and multiunit activity recordings in Te2 and BLA of rats that underwent recall at 24 h and 30 d after the association of an acoustic conditioned (CS, tone) and an aversive unconditioned stimulus (US, electric shock). Here we show that, during the recall of remote auditory threat memories in rats, the activity of the Te2 and BLA is highly synchronized in the theta frequency range. This functional connectivity stems from memory consolidation processes because it is present during remote, but not recent, memory retrieval. Moreover, the observed increase in synchrony is cue and region specific. A preponderant Te2-to-BLA directionality characterizes this dialogue, and the percentage of time Te2 theta leads the BLA during remote memory recall correlates with a faster latency to freeze to the auditory conditioned stimulus. The blockade of this information transfer via Te2 inhibition with muscimol prevents any retrieval-evoked neuronal activity in the BLA and animals are unable to retrieve remote memories. We conclude that memories stored in higher-order sensory cortices drive BLA activity when distinguishing between learned threatening and neutral stimuli.
  
  
  CONCLUSIONS
  How and where in the brain do we store the affective/motivational significance of sensory stimuli acquired through life experiences? Scientists have long investigated how "limbic" structures, such as the amygdala, process affective stimuli. Here we show that retrieval of well-established threat memories requires the functional interplay between higher-order components of the auditory cortex and the amygdala via synchrony in the theta range. This functional connectivity is a result of memory consolidation processes and is characterized by a predominant cortical to amygdala direction of information transfer. This connectivity is predictive of the animals' ability to recognize auditory stimuli as aversive. In the absence of this necessary cortical activity, the amygdala is unable to distinguish between frightening and neutral stimuli.
authors: Rita Levi-Montalcini Department of Neuroscience, University of Turin, I-10125 Turin, Italy.
authors: Marco
authors: http://orcid.org/0000-0002-0109-012X
authors: M
authors: Cambiaghi
authors: Rita Levi-Montalcini Department of Neuroscience, University of Turin, I-10125 Turin, Italy.
authors: Anna
authors: A
authors: Grosso
authors: Department of Biological Sciences, Hunter College, City University of New York, New York, New York 10065 and Biology Program, Neuroscience Collaborative, Graduate Center, City University of New York, New York, New York 10016.
authors: Ekaterina
authors: E
authors: Likhtik
authors: Institute of Neuroscience, Consiglio Nazionale delle Ricerche, Pisa 56124, Italy.
authors: Raffaele
authors: http://orcid.org/0000-0001-5344-5079
authors: R
authors: Mazziotti
authors: Rita Levi-Montalcini Department of Neuroscience, University of Turin, I-10125 Turin, Italy.
authors: Giulia
authors: G
authors: Concina
authors: Rita Levi-Montalcini Department of Neuroscience, University of Turin, I-10125 Turin, Italy.
authors: Annamaria
authors: A
authors: Renna
authors: Rita Levi-Montalcini Department of Neuroscience, University of Turin, I-10125 Turin, Italy.
authors: Tiziana
authors: T
authors: Sacco
authors: Department of Psychiatry, College of Physicians and Surgeons, Columbia University, New York, New York 10032, and.
authors: Joshua A
authors: JA
authors: Gordon
authors: Rita Levi-Montalcini Department of Neuroscience, University of Turin, I-10125 Turin, Italy, National Institute of Neuroscience-Corso Raffaello 30, I-10125 Turin, Italy benedetto.sacchetti@unito.it.
authors: Benedetto
authors: http://orcid.org/0000-0002-8695-8310
authors: B
authors: Sacchetti
mesh_terms: D000161:Acoustic Stimulation / Q000009:adverse effects* / Q000379:methods; D000818:Animals; D066272:Basolateral Nuclear Complex / Q000502:physiology*; D005239:Fear / Q000502:physiology* / Q000523:psychology; D007858:Learning / Q000502:physiology; D008297:Male; D008568:Memory / Q000502:physiology; D011939:Mental Recall / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013216:Reflex, Startle / Q000502:physiology*; D013003:Somatosensory Cortex / Q000502:physiology*
keywords: auditory cortex; basolateral amygdala; fear memory; memory consolidation; remote memory; theta activity