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Volume 1. Issue 3: July/August 2007 |
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Questions from the Field
Acoustic Startle Reflex
Researchers studying the acoustic startle reflex often wonder what units their data should be expressed in. Most commercial systems designed to measure the acoustic startle reflex use a sensor to convert the animal’s movement into a digital signal that is analyzed by the computer. Various methods exist for calibrating such sensors, and various types of sensors can be used, but usually startle responses are quantified in terms of “Arbitrary Units,” “Startle Units,” “Startle Response”, “A/D Units,” or some other similar designation (e.g. Bortolato et al, 2007; Jaworski et al, 2005; Meloni et al, 2006; Risbrough & Geyer, 2005; Vinkers et al, 2007; Winslow, Noble, & Davis, 2007). The within-subjects design of startle experiments indicates that such modes of quantitation are usually acceptable, independent of the specific vendor of the startle apparatus. The most important consideration for the researcher is that a standard calibration procedure be adopted that ensures similar sensitivities among all the startle sensors in his/her system.
| Q: What are the units for data gathered using SOF-825 Startle Reflex software? |
We are often asked what units the actual data from the startle sensor are expressed in. Med Associates’ most popular software for measuring the startle reflex response is called “Startle Reflex” (SOF-825). Startle Reflex software utilizes a highly sensitive analog-to-digital converter that converts the analog voltage signal from the startle sensor to a digital unit having a value between –2048 and +2048. The converter can handle voltages between –10 Volts and +10 Volts. In most cases, people simply leave their startle responses expressed on a scale of 0 to 2048 “Arbitrary Units” or “Startle Response Units” (e.g. Bortolato et al, 2007; Jaworski et al, 2005; Meloni et al, 2006). However, these values can be easily converted to a dimensioned quantity, such as Voltage.
Recalling the principles of operation described above, you can simply divide your startle response by 2048, and multiply this number by 10.
This process would yield the actual voltage measured by the analog-to-digital converter. This value can serve to instill confidence that similar sensitivities are achieved across all of your startle chambers. However, it is still difficult to compare actual data from different publications, unless you know specific calibration procedures that were used to generate the data of interest. We advocate publishing as much detail as possible regarding calibration methods. This allows researchers in different labs to make the most informative conclusions about the reported data, regardless of the units that the data are expressed in.
References:
Bortolato M, Frau R, Orru M, Piras AP, Fa M, Tuveri A, Puligheddu M, Gessa GL, Castelli MP, Mereu G, Marrosu F. Activation of GABA(B) receptors reverses spontaneous gating deficits in juvenile DBA/2J mice. Psychopharmacology (Berl). 2007 Jun 29; DOI 10.1007/s00213-007-0845-5.
Jaworski DM, Boone J, Caterina J, Soloway P, Falls WA. Prepulse inhibition and fear-potentiated startle are altered in tissue inhibitor of metalloproteinase-2 (TIMP-2) knockout mice. Brain Res. 1051(1-2):81-89, 2005.
Meloni EG, Jackson A, Gerety LP, Cohen BM, Carlezon WA. Role of the bed nucleus of the stria terminalis (BST) in the expression of conditioned fear. Ann. N. Y. Acad. Sci. 1071:538-541, 2006.
Risbrough VB, Geyer MA. Anxiogenic treatments do not increase fear-potentiated startle in mice. Biol. Psychiatry. 57(1):33-43, 2005.
Vinkers CH, Risbrough VB, Geyer MA, Caldwell S, Low MJ, Hauger RL. Role of dopamine D1 and D2 receptors in CRF-induced disruption of sensorimotor gating. Pharmacol. Biochem. Behav. 86(3): 550-558, 2007.
Winslow JT, Noble PL, Davis M. Modulation of fear-potentiated startle and vocalizations in juvenile rhesus monkeys by morphine, diazepam, and buspirone. Biol. Psychiatry. 61(3):389-395, 2007.
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