Fear-related signals in the primary visual cortex

Neuronal responses in the primary visual cortex (V1) are driven by simple stimuli, butthese stimulus-evoked responses can be markedly modulated by non-sensory factorssuch as attention and reward [1] and shaped by perceptual training [2]. In real-lifesituations, neutral visual stimuli can become emotionally tagged by experience,resulting in altered perceptual abilities to detect and discriminate these stimuli [3-5].Human imaging [4] and electroencephalography (EEG) studies [6-9] have shown thatvisual fear learning (the acquisition of aversive emotion associated with a visualstimulus) affects the activities in visual cortical areas as early as V1. However, itremains elusive whether the fear-related activities seen in the early visual cortex haveto do with feedback influences from other cortical areas; it is also unclear whether andhow the response properties of V1 cells are modified during the fear learning. In thecurrent study, we addressed these issues by recording from V1 of awake monkeysimplanted with an array of microelectrodes. We found that responses of V1 neuronswere rapidly modified when a given orientation of grating stimulus was repeatedlyassociated with an aversive stimulus. The output visual signals from V1 cells conveyed,from their response outset, fear-related signals that were specific to the fear-associatedgrating orientation and visual-field location. The specific fear signals were independentof neurons’ orientation preferences and were present even though the fear-associatedstimuli were rendered invisible. Our findings suggest a bottom-up mechanism thatallows for proactive labeling of visual inputs that are predictive of imminent danger.</p

Expression of <i>AtEXP2</i> in response to paclobutrazol treatment.

<p><i>AtEXP2</i> expression was determined by quantitative real-time RT-PCR in 24 h imbibed seeds treated with 10 µM PAC or without (Mock). Error bars represent SD. A Student’s t-test was calculated at the probability of 5% (*P<0.05).</p

Relative expression levels of <i>AtEXP2</i> in <i>exp2</i> and <i>35S:AtEXP2</i> line.

<p>Seeds of wild type, <i>exp2</i> and <i>35S:AtEXP2</i> overexpression line were harvested for RNA extraction after 24 h imbibition in water. Transcript abundance was measured by real-time RT-PCR and the values were normalized against the levels of <i>TUB2</i> as a housekeeping gene. Error bars represent SD.</p

Expression of <i>AtEXP2</i> in response to salt and osmotic stresses during seed germination.

<p>Col-0 seeds were collected 24 h after imbibition in different concentrations of NaCl, sucrose and mannitol. Error bars represent SD. A Student’s t-test was calculated at the probability of 1% (**P<0.01).</p

Germination phenotype of the wild type, <i>exp2</i> and <i>35S:AtEXP2</i> line.

<p>Non-dormant seeds of wild type, <i>exp2</i> and <i>35S:AtEXP2</i> overexpression line were employed in the germination assay. The germination frequencies were scored daily until the 7th day after sown. Error bars represent SD. A Student’s t-test was calculated at the probability of either 5% (*P<0.05) or 1% (**P<0.01).</p

Germination phenotype of the wild type, <i>exp2</i>, and <i>35S:AtEXP2</i> line in response to abiotic stresses.

<p>Seeds of wild type, <i>exp2</i> and <i>35S:AtEXP2</i> line were treated with different concentrations of NaCl (100 or 200 mM), sucrose (150 or 250 mM) and mannitol (200 or 400 mM). Error bars represent SD. A Student’s t-test was calculated at the probability of either 5% (*P<0.05) or 1% (**P<0.01).</p

Effects of DELLA on <i>AtEXP2</i> expression during seed germination.

<p>Expression level of <i>AtEXP2</i> was measured in 24 h imbibed seeds of wild type, <i>ga1-3</i>, and various <i>DELLA</i> mutants. <i>penta</i> indicates the <i>ga1-3 gai-t6 rga-t2 rgl1-1 rgl2-1</i> mutant. Error bars represent SD. A Student’s t-test was calculated at the probability of 1% (**P<0.01).</p

Expression pattern of <i>AtEXP2</i> gene.

<p>(A) Tissue-specific expression of <i>AtEXP2</i>. Various tissues of <i>Arabidopsis</i> wild type plants were harvested for RNA extraction. (B) Time course of <i>AtEXP2</i> expression. Dry seeds and imbibed seeds of Col-0 were harvested for RNA extraction. Transcript levels of <i>AtEXP2</i> were measured by real-time RT-PCR, and the values were normalized against the levels of <i>TUB2</i> as a control. Error bars represent SD. (C) GUS staining in germinating seeds of the <i>pAtEXP2:GUS</i> transgenic line. Seeds from T₃ homozygous plants of the <i>pAtEXP2:GUS</i> transgenic line were analyzed. Bar = 1 mm.</p

Expression of <i>AtEXP2</i> in response to exogenous GA application.

<p>Col-0 wild type seeds were harvested 4 h, 6 h and 8 h after imbibition in 10 µM GA₃ solution for RNA extraction respectively. Transcript levels were measured by real-time RT-PCR, and the values were normalized against the levels of <i>TUB2</i> as a control. Error bars represent SD. A Student’s t-test was calculated at the probability of 1% (**P<0.01).</p

Germination phenotype of the wild type, <i>exp2</i> and <i>35S:AtEXP2</i> line in response to GA and PAC treatment.

<p>Seeds of wild type, <i>exp2</i> and <i>35S:AtEXP2</i> line were treated with 10 µM GA₃ (A), 1 µM (B) or 5 µM (C) paclobutrazol (PAC). Error bars represent SD. A Student’s t-test was calculated at the probability of either 5% (*P<0.05) or 1% (**P<0.01).</p