The cognitive functions of the caudate nucleus
Introduction
Traditionally the basal ganglia have been associated with motor processes, although evidence for their role in parallel cognitive functions is mounting (for a review, see Middleton and Strick, 2000). In this review we are concerned with the striatum, composed of the putamen (or medial dorsal striatum in rodents) and the caudate nucleus (or lateral dorsal striatum). In particular, we focus on human, non-human primate, and rodent investigations in order to define the cognitive functions of the striatum, and especially to differentiate the functions of the caudate from those of the putamen.
The different roles of the caudate and putamen in higher level learning and memory tasks have been examined in animals using behavioural, lesion, and pharmacological techniques. In humans, a common approach for investigating the function of these areas has been to study the deficits that accompany basal ganglia pathology such as that found in Parkinson’s disease (PD) and Huntington’s disease (HD). In addition, recent functional neuroimaging studies using Positron Emission Tomography (PET) and functional magnetic resonance imaging (fMRI) have provided important new insights into striatal structure and function in the healthy human brain. Pharmacological manipulations have also been conducted to investigate the role of dopamine, a neurotransmitter that is crucial to normal striatal function, in cognitive tasks involving the caudate.
In this review, we consider converging evidence from multiple domains and conclude that the caudate plays a critical role in supporting the planning and execution of strategies and behaviour required for achieving complex goals, i.e. in action-outcome learning that subserves goal-directed action. This is in contrast to the putamen, which appears to subserve cognitive functions more limited to stimulus-response, or habit, learning.
Section snippets
Basal ganglia anatomy
In humans and non-human primates, the basal ganglia comprise the striatum (the caudate and the putamen, linked together through the fundus), the ventral striatum (the nucleus accumbens and most ventral aspects of caudate and putamen), the globus pallidus (internal and external sectors), the substantia nigra, and the subthalamic nucleus (Nolte, 1999). In non-primates the anatomy is similar. For the purpose of this cross-species review the dorsal striatum (DS) in rats will be considered to
Animal research into striatal function
Historically, two seemingly disparate models of dorsal striatal function have emerged from animal research: (1) the conception of the striatum as a habit mechanism, and (2) the conception of the striatum as a mechanism for flexibility and switching. It is becoming clear that different components of the striatum (corresponding to the putamen/lateral dorsal striatum and caudate/medial dorsal striatum, respectively) may contribute to both of these processes within the broader framework of distinct
Parkinson’s disease as a model for examining caudate dysfunction in humans
Parkinson’s disease (PD) is probably the most-studied of all the basal ganglia disorders, and as such, is a principal source of information about human striatal function. Patients with PD develop deficits across a wide range of cognitive functions, including memory, attention, planning, and skill learning. Many of these functions are crucial for guiding action in the pursuit of goals.
Methodology
Although clues about the functions of the caudate nucleus can be gleaned from comparisons between patients with PD (or HD) and patients with frontal-lobe damage, it is not possible to delineate the exact contributions of different striatal regions to behaviour on the basis of studies in patients alone as, even in the early stages of disease, the pathology in these neurodegenerative conditions is undoubtedly somewhat distributed and likely involves a number of anatomical regions and
Conclusions
It is widely accepted that the basal ganglia as a whole are broadly responsible for sensorimotor coordination, including response selection and initiation. However, it has become increasingly clear that regions of the striatum can be functionally delineated along corticostriatal lines and the convergence of several research domains, including anatomical studies of corticostriatal circuitry, neuroimaging studies of healthy volunteers, patient studies of performance deficits on a variety of
References (158)
- et al.
Functional architecture of basal ganglia circuits—neural substrates of parallel processing
Trends Neurosci.
(1990) Neural bases of food-seeking: affect, arousal and reward in corticostriatolimbic circuits
Physiol. Behav.
(2005)- et al.
Goal-directed instrumental action: contingency and incentive learning and their cortical substrates
Neuropharmacology
(1998) - et al.
Brain dopamine and the syndromes of Parkinson and Huntington. Clinical, morphological and neurochemical correlations
J. Neurol. Sci.
(1973) - et al.
Functional imaging of neural responses to expectancy and experience of monetary gains and losses
Neuron
(2001) - et al.
The relation of putamen and caudate nucleus 18F-Dopa uptake to motor and cognitive performances in Parkinson’s disease
J. Neurol. Sci.
(1999) - et al.
How common is dementia in Parkinson’s disease?
Lancet
(1984) - et al.
Positron emission tomography shows that impaired frontal lobe functioning in Parkinson’s disease is related to dopaminergic hypofunction in the caudate nucleus
Neurosci. Lett.
(2001) - et al.
Ordinal, phase, and interval timing
- et al.
Inactivation of the infralimbic prefrontal cortex reinstates goal-directed responding in overtrained rats
Behav. Brain Res.
(2003)