Young, A. H. | bioRxiv Science

bioRxiv2026

Hoverfly responses to looming stimuli depend on elevation and speed

An object on immediate collision course generates a rapidly expanding visual stimulus on the retina, which will typically trigger a fast reaction, such as an evasive behavior. In hoverflies, for example, visual looming stimuli may be generated if the insect is about to collide with a stationary object in the surround, by an approaching predator, or by conspecifics during territorial interactions. Supporting these behavioral responses is a diverse range of looming sensitive descending neurons that project information from the optic lobes and central brain to the motor control centers in the thoracic ganglia. We here show that the looming sensitive descending neurons are predominantly sensitive to looming stimuli located in the ventral visual field. To investigate if this is matched by behavior, we recorded how tethered hoverflies responded to looming stimuli presented dorsally or ventrally on a visual monitor, at four different speeds (l/|v| of 10 - 667 ms), covering a naturalistic range. We found that ventral stimuli, especially at intermediate speeds (l/|v| = 50 or 200 ms), triggered much stronger behavioral responses than dorsally displayed stimuli. The behavioral data thus not only match the receptive fields of the neurons likely to support the behavior, but also highlight that behavioral output is not entirely reflexive but is strongly modulated by stimulus speed and elevation. Significance StatementIf someone throws a ball at you, this generates a rapidly expanding object across your visual field, which will make you react before you have even had time to think. You may for example duck, dip or dive to avoid the ball, or bring your hands up to grab it. Similarly, many insects respond to rapidly approaching objects. We here show that hoverfly reactions to such looming stimuli depend on stimulus speed and elevation, with the strongest response to stimuli approaching from below. We further demonstrate that the neurons likely supporting these behaviors show highest sensitivity in the ventral visual field, suggesting a close match between neural tuning and behavioral output.

animal behavior and cognition↗

bioRxiv2025

The effect of psychedelics on associative learning: a systematic review

IntroductionPsychedelics are emerging as potential treatments for neuropsychiatric conditions, with evidence suggesting a single administration can lead to enduring behavioural changes. While the underlying putative mechanism(s) remain unclear, there is evidence supporting altered learning as a key candidate. AimThis systematic review examined studies assessing the effects of psychedelics on associative learning in both humans and animals. MetodsElectronic databases were searched up until 13/01/2025 for studies investigating any difference in learning after psychedelic administration. Results31 studies were included (29 in animals, 2 in humans). Classical and operant conditioning paradigms were employed, including fear extinction, conditioned avoidance, and reversal learning. Studies assessed acute and post-acute effects, however repeated dosing paradigms often obscured this distinction. There was considerable heterogeneity in study designs, paradigms, drug administration timings and doses, and behavioural effects appeared to be influenced by dose, timing, training intensity, and sex. Due to between-study heterogeneity, a meta-analysis was not possible. Evidence suggests that psychedelic administration enhances associative learning in animals across paradigms, although findings were not entirely consistent. Possible mechanisms identified were increased prediction error sensitivity, serotonin receptor agonism, and structural plasticity. Learning enhancements may extend into the post-acute phase and appear to depend on active environmental engagement during this window. ConclusionStudies suggest that psychedelics enhance associative learning in animals; however, these findings are yet to be translated into humans. Understanding whether a period of enhanced learning follows the psychedelic experience may have important implications for psychedelic-assisted psychotherapy, where behavioural changes must generalise and persist beyond the drug-induced state.

neuroscience↗

bioRxiv2018

Comparative efficacy and acceptability of non-surgical brain stimulation for the acute treatment of adult major depressive episodes: A systematic review and network meta-analysis of 113 randomised clinical trials

Background: Non-surgical brain stimulation techniques have been applied as tertiary treatments in major depression. However, the relative efficacy and acceptability of individual protocols is uncertain. Our aim was to estimate the comparative clinical efficacy and acceptability of non-surgical brain stimulation for the acute treatment of major depressive episodes in adults.\n\nMethods: Embase, PubMed/MEDLINE and PsycINFO were searched up until May 8, 2018, supplemented by manual searches of bibliographies of recent reviews and included trials. We included clinical trials with random allocation to electroconvulsive therapy (ECT), repetitive transcranial magnetic stimulation (rTMS), accelerated TMS (aTMS), priming TMS (pTMS), deep TMS (dTMS), theta burst stimulation (TBS), synchronised TMS (sTMS), magnetic seizure therapy (MST) or transcranial direct current stimulation (tDCS) protocols or sham. Data were extracted from published reports and outcomes were synthesised using pairwise and network random-effects meta-analysis. Primary outcomes were response (efficacy) and all-cause discontinuation (acceptability). We computed odds ratios (OR) with 95% confidence intervals (CI). Remission and continuous post-treatment depression severity scores were also examined.\n\nResults: 113 trials (262 treatment arms) randomising 6,750 patients (mean age = 47.9 years; 59% female) with major depressive disorder or bipolar depression met our inclusion criteria. In terms of efficacy, 10 out of 18 treatment protocols were associated with higher response relative to sham in network meta-analysis: bitemporal ECT (OR=8.91, 95%CI 2.57-30.91), high-dose right-unilateral ECT (OR=7.27, 1.90-27.78), pTMS (OR=6.02, 2.21-16.38), MST (OR=5.55, 1.06-28.99), bilateral rTMS (OR=4.92, 2.93-8.25), bilateral TBS (OR=4.44, 1.47-13.41), low-frequency right rTMS (OR=3.65, 2.13-6.24), intermittent TBS (OR=3.20, 1.45-7.08), high-frequency left rTMS (OR=3.17, 2.29-4.37) and tDCS (OR=2.65, 1.55-4.55). Comparing active treatments, bitemporal ECT and high-dose right-unilateral ECT were associated with increased response. All treatment protocols were at least as acceptable as sham treatment.\n\nConclusion: We found that non-surgical brain stimulation techniques constitute viable alternative or add-on treatments for adult patients with major depressive episodes. Our findings also highlight the need to consider other patient and treatment-related factors in addition to antidepressant efficacy and acceptability when making clinical decisions; and emphasize important research priorities in the field of brain stimulation.\n\nO_LSTTreatment abbreviationsC_LSTECT = Electroconvulsive Therapy O_LIBF ECT = bifrontal ECT (1)\nC_LIO_LIBT ECT = bitemporal ECT (2)\nC_LIO_LIRUL ECT= right unilateral ECT O_LIH-RUL = high-dose RUL ECT (3)\nC_LIO_LILM-RUL = low to moderate-dose RUL ECT (4)\nC_LI\nC_LI\nrTMS = repetitive Transcranial Magnetic Stimulation O_LIHF-L rTMS = high-frequency rTMS of the left DLPFC (5)\nC_LIO_LIHF-R rTMS = high-frequency rTMS of the right DLPFC (6)\nC_LIO_LILF-R rTMS = low-frequency rTMS of the right DLPFC (7)\nC_LIO_LILF-L rTMS = low-frequency rTMS of the left DLPFC (8)\nC_LIO_LIBL rTMS = bilateral rTMS of the DLPFC (9)\nC_LI\ndTMS = deep Transcranial Magnetic Stimulation (10)\npTMS = priming Transcranial Magnetic Stimulation (11)\naTMS = accelerated Transcranial Magnetic Stimulation (12)\nsTMS = synchronised Transcranial Magnetic Stimulation (13)\nTBS = Theta Burst Stimulation O_LIiTBS = intermittent TBS of the left DLPFC (14)\nC_LIO_LIcTBS = continuous TBS of the right DLPFC (15)\nC_LIO_LIblTBS = bilateral TBS of the DLPFC (16)\nC_LI\nMST = Magnetic Seizure Therapy (17)\ntDCS = transcranial Direct Current Stimulation (18)\n\n\nKey points\n\nQuestion: What is the clinical efficacy and acceptability of non-surgical brain stimulation protocols for the acute treatment of major depressive episodes in adults?\n\nFindings: In this network meta-analysis, 10 out of 18 treatment protocols were associated with higher response rates relative to sham, most notably bitemporal and high-dose right unilateral electroconvulsive therapy. All treatment protocols were at least as acceptable as sham treatment.\n\nMeaning: Non-surgical brain stimulation techniques constitute viable alternative or add-on treatment strategies for adult patients with major depressive episodes.

neuroscience↗