Origin of STn Overactivity in PD

The STn plays a key role in the basal ganglia circuitry, and its hyperactivity may be a major factor in parkinsonian symptomatology (Marsden and Obeso, 1994). According to the classical PD model, it is the hypoactivity of the GPe that leads to increased STn activity, which in turn (in addition to the diminished influence of the direct striatal GABAergic input) induces the pathological overactivity of GPi (Figure 20.6). However, although stimulation of the STn induces a strong activation of GPe...

Cnv Topography And Generators

Stimulus Preceding Negativity

The primary source of evoked potentials is neuronal activity in the upper layers of the cortex. It is primarily the simultaneous occurrence of numerous excitatory postsynaptic potentials at apical dentrites of pyramidal neurons close to the recording electrode that causes changes in the evoked potentials at the surface of the head (Birbaumer et al., 1990). Most studies report that the CNV is mainly observed at fronto-central, central, and centro-parietal regions. However, it is sometimes...

The Importance Of Interval Timing In Memory And Attention

Human learning and memory is also highly sensitive to temporal factors, and oscillator-based models have been proposed for the coding of serial order in memory (e.g., Brown and Chater, 2001 Brown et al., 2000 McCormack and Hoerl, 2001). In addition, deficits in learning, memory, set shifting, and interval timing have been observed in a variety of patient populations with damage to the basal ganglia, including Parkinson's disease and Huntington's disease patients, as well as other cortical and...

Functional Anatomy Account A Revised Model Of The Basal Ganglia

Overactivity of the STn is seen by the classical PD model as a key abnormality underlying parkinsonian symptoms in human and nonhuman primates (Albin et al., 1989 DeLong, 1990). However, the evidence not only remains controversial, but also is for the most part restricted in motor deficits. A cartoon illustration of this model is shown in Figure 20.6. Like any model, the classical Albin-DeLong model of the basal ganglia is limited, because it is trying to simplify the complex reality (Chesselet...

Mechanisms Underlying Modality Effects In Time Perception

Pacemaker Switch Accumulator System

The following section outlines some of the evidence suggesting that there are latency differences in signal detection or differences in clock speed between the visual and auditory modalities. As noted above, both timing onset-offset latency and clock speed have been proposed as putative mechanisms underlying modality differences. Evidence that the response time RT for an auditory stimulus is shorter than that for a visual stimulus, by about 40 msec, comes from experiments showing that in order...

Connections Between Interval Timing Neuropharmacology And Drug Abuse

Drugs that increase the effective level of dopamine in the brain, such as cocaine and methamphetamine, are among the most commonly abused drugs today Stahl, 2000 . The connection between interval timing and drug abuse comes from the fact that dopaminergic drugs cause predictable distortions in timing and time perception. The dopamine agonist, methamphetamine, causes a leftward shift in psychophysical timing functions that is proportional in size to the duration of the interval being timed e.g.,...