What are slices in fMRI?
Unlike a photograph, in which the entire picture is taken in a single moment, an fMRI volume is acquired in slices. Each of these slices takes time to acquire – from tens to hundreds of milliseconds. The two most commonly used methods for creating volumes are sequential and interleaved slice acquisition.
What is slice timing in fMRI?
Most fMRI data are acquired using two-dimensional pulse sequences that acquire images one slice at a time, thus all slices are acquired at different time within a repeat time (TR).
What is fMRI acquisition?
Typically, fMRI data are acquired using a series of 2D axial slices to cover the whole brain (one volume) and then the process is repeated to collect a number of volumes over time (time-series). Each volume can be acquired using either interleaved or sequential slice acquisitions.
How many pieces are in a fMRI?
How many slices? The default of 32 slices will cover most of the brain in most subjects. However, if you are also interested in the cerebellum, 36 slices is recommended (this results in a 2.19 second TR).
What is slice acquisition?
In order to collect data from the entire brain, a typical pulse sequence might acquire 30 (or more) slices throughout the TR (e.g. 3s). One approach is to use ascending/descending slice acquisition, in which slice are collected consecutively.
What is slice timing correction?
Slice timing correction (STC) is the preprocessing step applied to correct for these slice-dependent delays, achieved by shifting the time series of each slice to temporally align all slices to a reference time-point.
How do I preprocess fMRI data?
So there are a number of different preprocessing steps, and they include visualization, and artifact removal, slice time correction, motion correction, correction for physiological effects, co-registration and normalization, and spatial and temporal filtering.
What is motion correction?
Motion correction is performed by mapping each slice to an anatomic volume data set acquired in the same fMRI session to accommodate inter-slice head motion. Accuracy of the registration parameters was assessed by registration of simulated MR data of the known truth.
What is reverse inference?
Abstract. Reverse inference in cognitive neuropsychology has been characterized as inference to ‘psychological processes’ from ‘patterns of activation’ revealed by functional magnetic resonance or other scanning techniques.
What is double dissociation in memory?
a research process for demonstrating the action of two separable psychological or biological systems, such as differentiating between types of memory or the function of brain areas. One experimental variable is found to affect one of the systems, whereas a second variable affects the other.
What is reverse inference neuroscience?
In general, reverse inference allows the determination of the extent to which a certain brain activation is indicative of the involvement of a specific cognitive process (thereafter abbreviated as “the activation” and “the process”).
What is reverse inference fMRI?
Reverse inference, i.e. the use of brain activation (fMRI) data to infer the engagement of a certain mental function, is heavily criticised (e.g., Poldrack 2011, Neuron).